Children and adolescents with Autism Spectrum Disorder (ASD) often show comorbid emotional and behavior problems. The aim of this longitudinal study is to examine the relation between emotion control (i.e., negative emotionality, emotion awareness, and worry/rumination) and the development of internalizing and externalizing problems. Boys with and without ASD (N = 157; age 9-15) were followed over a period of 1.5 years (3 waves). We found that baseline levels of worry/rumination was a specific predictor of later externalizing problems for boys with ASD. Furthermore, the developmental trajectory of worry/rumination predicted the development of internalizing and externalizing problems in both groups. Our findings suggest that worry/rumination may constitute a transdiagnostic factor underlying both internalizing and externalizing problems in boys with and without ASD.