Children with autism have an increased risk for obstetric complications but it is not known whether these are of primary aetiological significance. It is also unclear whether obstetric complications play a secondary role in shaping phenotypic expression in individuals at genetic risk for autism. We investigated this question by studying the role of obstetric complications in determining phenotypic manifestations in tuberous sclerosis, a single gene disorder frequently associated with autism spectrum disorders. Obstetric histories of 43 children with non-familial TS and 40 unaffected siblings were obtained using a structured parent interview. ADI-R, ADOS-G and IQ evaluations were undertaken. Children with TS experienced more obstetric complications than their unaffected siblings, but these were related to mild rather than severe adversities. No differences in obstetric complications were found in children with and without autism spectrum disorders and there was no positive correlation between obstetric adversities and severity of autism spectrum disorders or intellectual impairments.