My autistic child has a large head. Should I be worried?

Many parents notice that their autistic child has a big head. Sometimes a health visitor or doctor mentions it first. This page explains what doctors measure, how often it happens in autism, and when a genetic test is offered.

What counts as a large head?

Doctors measure the distance around the head, just above the eyebrows and ears. This is called the head circumference. They plot it on a growth chart for your child's age.

The medical word for a large head is macrocephaly. Sources do not agree on one exact cut-off. Doctors usually call a head large when it measures above the 97th to 98th centile for age, or 2 standard deviations (SD) above average. A standard deviation is a measure of how far a value sits from the average. Some guidance uses a higher cut-off of 3 SD.

So there is no single rule. Your child's doctor will look at the chart, not one number.

How common is it in autism?

A large review in 2015 pooled 27 studies. It found that 822 of 5,225 autistic people had a large head. That is about 16 %, or about 1 in 6. By definition, only about 2 to 3 % of all people sit above the 97th to 98th centile.

Head size and brain size were larger mainly in early childhood.

If you want to read about the research on why brains grow differently in some autistic children, see what brain organoids tell us about macrocephaly.

Often it runs in the family

A large head on its own, in a child with no other developmental or health concerns, may simply run in the family. This is why doctors should measure the parents' heads too. If a parent also has a large head, that is useful information.

What the doctor checks at the autism assessment

NICE (the National Institute for Health and Care Excellence) writes guidance for the NHS (National Health Service). Its autism guideline for children, CG128, recommends a physical examination as part of the assessment (recommendation 1.5.6). This includes:

• checking for a large or small head
• checking for unusual physical features
• looking at the skin for signs of two genetic conditions, neurofibromatosis and tuberous sclerosis, sometimes with a special ultraviolet lamp called a Wood's light

If your child's head size was not measured at the assessment, it is reasonable to ask.

Where genes come in: PTEN

PTEN is a gene. A change in this gene can cause a condition called PTEN hamartoma tumour syndrome (PHTS). A large head is one of its main features.

Four small studies tested autistic children who had a large head, from clinics in the USA (Butler 2005, Varga 2009, McBride 2010, Klein 2013). Between 5 % and 22 % of these children had a PTEN change. The rate was highest in children with very large heads.

These figures come from small, selected clinic groups. They do not apply to all autistic children. In these studies, most autistic children with a large head did not have a PTEN change.

Testing on the NHS

There are two main NHS routes. Both are listed in the NHS National Genomic Test Directory.

R27: whole genome sequencing. This is for children with developmental delay or learning disability. It reads all of your child's genes, and PTEN is included. Paediatricians can now order this test directly. You can read more in genome sequencing for developmental delay.

R213: a PTEN test. This is for a large head together with other signs. These include certain skin signs, such as small bumps on the face, small growths in the mouth, thick patches on the hands or feet, or fatty lumps (lipomas). Other signs from the test criteria can also count. This route may need a referral to clinical genetics.

Autism on its own is not a reason for an R213 test. Your doctor has to see a large head plus other signs.

For an overview of genetic tests in the UK, see genetic testing for autism and ADHD in the UK. If you are wondering whether autism itself runs in families, see Autism and ADHD: is it genetic?

If a PTEN change is found

People with PHTS have a higher risk of some cancers later in life, mainly breast, thyroid and womb cancer. The risk of kidney and bowel cancer and melanoma is moderately raised.

This is why people with PHTS are offered regular checks. In Europe these follow a 2026 guideline from ERN GENTURIS, a European network for inherited tumour conditions. Your genetics team will explain which checks are needed and when. Please do not try to work out a schedule from this page.

In one study, relatives who carried the same change had a large head, learning disability or early cancer, and none had been diagnosed before. A result in a child can therefore help other family members too.

When to see a doctor sooner

UK children have relatively large heads compared with the World Health Organization (WHO) standard. The UK-WHO growth chart from the RCPCH (Royal College of Paediatrics and Child Health) says a large head should only cause concern if it keeps growing faster after 6 months of age, or if there are other signs or symptoms. The point to watch is a head above the 99.6th centile, or one that crosses upwards through 2 centile spaces.

Doctors also look for skin signs. These include café-au-lait (light brown) or pale patches, capillary haemangiomas (birthmarks made of blood vessels), and small lumps around the nose and mouth. They should measure the parents' heads too.

Contact a doctor the same day if your child has signs of raised pressure inside the head:

• a bulging fontanelle (the soft spot on a baby's head)
• vomiting
• unusual sleepiness or irritability
• eye changes, such as crossed eyes, a droopy eyelid or double vision
• problems with walking
• seizures
• loss of skills they had before

An Italian review (Accogli 2021) says doctors usually advise a brain scan when there are signs like these, other neurological signs, or concerns about development. A scan may not be needed when the child is otherwise well and other family members have large heads.

In short

• About 1 in 6 autistic people has a large head.
• Often it runs in the family. Ask for the parents' heads to be measured.
• A PTEN test is offered when there is a large head plus other signs, not for autism alone.
• If your child has developmental delay, whole genome sequencing (R27) includes PTEN.

Large head size can also sit alongside other physical differences that parents ask about, such as eating non-food items. See pica in autistic children.

References

1. Sacco R, Gabriele S, Persico AM. Head circumference and brain size in autism spectrum disorder: a systematic review and meta-analysis. Psychiatry Res Neuroimaging 2015;234(2):239–51. doi:10.1016/j.pscychresns.2015.08.016
2. Butler MG, Dasouki MJ, Zhou XP, Talebizadeh Z, et al. J Med Genet 2005;42(4):318–21. doi:10.1136/jmg.2004.024646
3. Varga EA, Pastore M, Prior T, Herman GE, McBride KL. Genet Med 2009;11(2):111–7. doi:10.1097/GIM.0b013e31818fd762
4. McBride KL, Varga EA, Pastore MT, Prior TW, et al. Autism Res 2010;3(3):137–41. doi:10.1002/aur.132
5. Klein S, Sharifi-Hannauer P, Martinez-Agosto JA. Autism Res 2013;6(1):51–6. doi:10.1002/aur.1266
6. Hoogerbrugge N, Blatnik A, Lautrup CK, et al. ERN GENTURIS cancer surveillance guideline for individuals with PTEN hamartoma tumour syndrome. Eur J Hum Genet 2026. doi:10.1038/s41431-026-02181-z
7. NICE CG128. Autism spectrum disorder in under 19s: recognition, referral and diagnosis. Recommendation 1.5.6. https://www.nice.org.uk/guidance/cg128/chapter/Recommendations
8. NHS England. National Genomic Test Directory, rare and inherited disease eligibility criteria v8.0 (May 2025): R27, R213. https://www.england.nhs.uk/wp-content/uploads/2018/08/rare-inherited-disease-eligibility-criteria-v8.0.pdf
9. NHS England Genomics Education Programme. GeNotes: Child with macrocephaly. https://www.genomicseducation.hee.nhs.uk/genotes/in-the-clinic/presentation-child-with-macrocephaly/
10. RCPCH. UK-WHO growth chart, boys 0–4 years: Interpreting the chart. https://www.rcpch.ac.uk/sites/default/files/Boys_0-4_years_growth_chart.pdf
11. Accogli A, Geraldo AF, Piccolo G, et al. Diagnostic approach to macrocephaly in children. Front Pediatr 2021;9:794069. doi:10.3389/fped.2021.794069