Autism and autism spectrum disorders (ASDs) are neurodevelopmental disorders characterised by the behavioral traits of impaired social cognition and communication, and repetitive and/or obsessive behaviour and interests. Studies point towards increased prevalence of autism/ASD. However, no treatment or prevention for the disorder has been established, since the aetiological pathway of this disorder remains largely unknown. Considering this lack of knowledge, epidemiological studies are expected to give clues for a better understanding of the disorder. As such, advanced paternal age at birth and low birthweight (or intrauterine growth retardation) have been reported to be candidate risk factors. These findings allow us to propose novel research strategies in search of the aetiology of autism/ASD. Following this trend, the authors initiated a research project, "the Hamamatsu Birth Cohort for Mothers and Children (HBC)", seeking risk factors for autism/ASD extensively. The HBC is expected to enroll 1,200 dyads of mother and child and to follow them until the child becomes 4 years of age.