This article critically reviews research done in the past 2 years concerning the pathophysiology and treatment of autism. Recent research in genetics, neuroimaging, neurochemistry, and pharmacologic treatment has advanced the body of knowledge about the pathophysiology of autism. Relatively new imaging technologies (eg, positron emission tomography) are increasingly being applied to the study of subjects with autism and have produced promising results that await replication. Neurochemical and challenge studies continue to suggest a role for 5-HT dysregulation in autism. Additional research is needed to determine the role of neuroendocrine and autoimmune factors in autism. Significant gains have been made in determining which pharmacologic treatments are efficacious in autism. Additional research is needed on agents that might ameliorate the core and associated symptoms of autism.