Autism is a pervasive neurodevelopmental disorder with prominent reciprocal social and communication impairment and restricted repetitive behavior or interest. Based on the number of symptoms and functional impairment, autistic disorder, Asperger disorder, and atypical autism (or PDDNOS) are conceptualized as the autism spectrum disorder (ASD). Most recent survey estimated the prevalence of narrow diagnosis of autistic disorder to be around 0.1% to 0.2%, and 0.59 % to 0.63% for ASD, with a four-fold male predominance. Due to high heritability (> 0.9), high family recurrence risk (λ = 60), and severe impairment without effective prevention and treatment available for ASD, this disastrous disease has been prioritized for molecular genetic study from public health perspective. The proposed research is the first systematic approach combining clinical and molecular genetic study of ASD involving multi-sites and three research cores: assessment core (by Gau SS and Wu YY), molecular genetics core (by Chen CH), and data/statistics core (by Gau SS).