There has been little research connecting underlying emotion processes (e.g., emotion regulation) to frequent behavior problems in young children with autism spectrum disorder (ASD). This study examined the stability of emotion regulation and its relationship with other aspects of child functioning. Participants included 108 children with ASD, ages 4-7, and their primary caregivers. ASD symptoms and cognitive/language abilities were assessed upon study entry. Parents reported on children's emotion regulation, social skills and behavior problems at two time points, 10 months apart. Emotion dysregulation was stable and related strongly to social and behavioral functioning but was largely independent of IQ. Further analyses suggested that emotion dysregulation predicts increases in social and behavioral difficulties across time. Implications for intervention are discussed.