Autism has the highest estimated heritability (>90%) among behaviorally defined neuropsychiatric disorders. Rapidly advancing genomic technologies and large international collaborations have increased our understanding of the molecular genetic causes of autism. Pharmacogenomic approaches are currently being applied in two single-gene disorders, fragile X syndrome and Rett syndrome, which capture many aspects of the autistic phenotype. This review describes the current state of the genetics of autism and suggests how to extend pharmacological principles pioneered in fragile X and Rett to the broader group of patients with autism.