Autism spectrum disorders (ASDs) are neurodevelopmental disorders characterized by impairment of reciprocal social interaction and communication and restricted repetitive behaviors.¹ They have persisting negative effects on learning and development of independence in adulthood.² In 2007, the yearly cost to society of each adult with ASD in Great Britain was estimated to be £90 000.³ Adults with ASDs are more likely to be recognized and supported if they also have severe intellectual disability; those with higher levels of functioning tend to be overlooked in the community.⁴

The study of sexual behaviour lies at the heart of understanding the transmission dynamics of sexually transmitted infections (STIs). Academic investigation into sexual behaviour dates back to the 18th century and, over time, has employed a variety of approaches including the medical and psychiatric investigation of sexual disorders, anthropological investigations, and survey research based largely on volunteer samples. More recent studies, driven largely by the public health response to HIV/AIDS, have focused on large scale probability sample survey research.^1–5 Key areas of inquiry have shifted towards describing population patterns of risk behaviours for STI/HIV transmission, understanding how epidemics of STIs are generated, and informing disease control strategies.