Temperament is important for considering differences among diagnostic groups and for understanding individual differences that predict problematic behavior. Temperament characteristics, such as negative affectivity, effortful control, and surgency (highly active and impulsive), are predictive of externalizing behavior in typically developing children, but these links have not been investigated among children with autism spectrum disorder (ASD). In the present study, the authors analyzed differences in temperament between children with ASD and neurotypical children, investigated the range of individual differences within our sample, and examined the relationship between temperament and problem behavior. A few differences in temperament between the ASD sample and reference sample were noted and considerable variability in temperament was observed across children with ASD. High negative affectivity, high surgency, and low effortful control were related to problem behavior as measured by parent questionnaire. The potential utility of temperament assessment in developing new intervention options for addressing problem behavior is discussed. (Contains 5 tables.)