Objective: Study familial and pre- and perinatal factors in Asperger Syndrome (AS). Methods: Hundred boys with AS had their records reviewed. "Pathogenetic subgroups" were defined according to presence of medical syndromes/chromosomal abnormalities, indices of familiarity, and pre- and perinatal risk factors predisposing to brain damage. Results: No major index of pathogenetic factors was found in 13%, a syndrome/chromosomal abnormality in 8%, pre- or perinatal risk 13%, combined pre- or perinatal risk and family history in 11%, and family history only in 55% Comment: About 50% of all boys with AS have a paternal family history of autism spectrum disorder. Pre- and perinatal risks appear to be important in about 25% cases.