The objective of this study was to investigate the background and associated factors in a representative group of young males with Asperger syndrome (AS) presenting at a specialized autism clinic. One hundred males aged 5 years 6 months to 24 years 6 months, with a mean age of 11 years 4 months (SD 3y 10mo), who had a clinical diagnosis of AS were included in the study. An in-depth review of their medical records and neuropsychological test data was performed. There was a high rate (51%) of non-verbal learning disability (defined as Verbal IQ more than 15 points higher than Performance IQ), but otherwise there was little or no support for the notion of right-hemisphere brain dysfunction being at the core of the syndrome. There was a very high rate of close relatives with autism spectrum problems, but also high rates of prenatal and perinatal problems, including prematurity and postmaturity. In comparison with general population data, those with AS very often had a combination of genetic and prenatal and perinatal risk factors. Non-verbal learning disability test results applied in about half the group. There was a subgroup of individuals with AS who had macrocephalus. However, there was no support for an association of AS with low body mass index.