Autism spectrum disorder (ASD) is defined by difficulties with social interaction and communication, and restricted or repetitive behaviors. It is more common in males than females. The causes are genetic and environmental factors that impact brain development. Symptoms usually appear by age 2. Diagnosis involves screening tools and observing behaviors. Treatment involves early intervention with intensive educational and behavioral therapies for at least 25 hours per week. Medications may help specific symptoms but do not treat the underlying condition. Prognosis is better with early identification and treatment.