Background HIV is known to cause neurodevelopmental problems in infants and young children. The impact of HIV on the development of preschool‐age children has been less well described. Method The study was conducted at an urban paediatric HIV clinic in Johannesburg, South Africa. A sample of convenience was used. Sixty‐eight medically stable children between the ages of 3 and 5 years were assessed with the Griffiths Scales of Mental Development. Children were excluded from the study if they had severe HIV encephalopathy, which made it impossible for them to participate in the items on the Griffiths Scales of Mental Development. Results The children had started combination antiretroviral treatment (cART) at a mean age of 8.1 months. The majority of the children were virologically suppressed and did not present with wasting or stunting. Severe overall developmental delay (z‐scores < −2SD) was detected in 55.88% of children. Developmental facets related to speech, cognition and perception were the most severely affected. Personal–social development was the least affected with only 13.4% of the children demonstrating severe delay. Conclusion Despite having early access to cART, children infected with HIV are still at risk for severe developmental delay across a number of facets. Very early initiation of cART may help alleviate this problem. All preschool children infected with HIV should have routine developmental screening.