The aims of the present study were to describe variations in the early course of development in autism by utilizing an in-depth parent interview that incorporated techniques to improve accuracy of parent recall, and to examine the relation between variations in early developmental course in autism and behavioral outcome at 3-4 years of age. The Early Development Interview, which consisted of questions about child's behavior in several domains from birth through 2 years of age, was created and administered to parents of 72 3-4-year-old children with autism spectrum disorder and 34 3-4-year-old children with developmental delay, who were matched on mental and chronological age, and 39 1-4-year-old typically developing children, who were matched to the clinical groups on mental age. At 3-4 years of age, children were administered standardized measures (some clinician administered and some parent report); these included verbal and nonverbal IQ, autism symptom severity, and adaptive and aberrant behavior. Based on the Early Development Interview, children with autism spectrum disorder (ASD) were reported to have elevated symptoms in the social and regulatory domains by 3-6 months. By 12-15 months, parents of children with ASD reported significantly higher levels of social symptoms than parents of children with developmental delay. At 3-4 years of age, children with autism with early vs. late onset of symptoms, and with vs. without a history of loss of skills (regression) were not found to differ on standardized tests of verbal and nonverbal IQ and observational measures of autism symptom severity.