Difficulties regulating emotion have been linked to comorbid psychopathology in children with autism spectrum disorder (ASD), but little empirical work has examined predictors of dysregulation in this population. Forty-six families of children with ASD participated in a laboratory visit that included direct measurement of children's IQ, ASD symptoms, and psychophysiological reactivity. Child emotion regulation was observed during independent and co-regulatory tasks, and parental scaffolding was rated in the dyadic context. ASD symptom severity emerged as the strongest predictor of child emotion dysregulation across contexts. Child age and parental scaffolding also uniquely predicted child dysregulation in the dyadic task. Implications for conceptualizing intrinsic and extrinsic influences on emergent emotion regulation in children with ASD are discussed, as are applications to intervention.