Understanding hetereogeneity in symptom expression across the autism spectrum disorders (ASD) is a major challenge for identifying causes and effective treatments. In 40 children and adolescents diagnosed with ASD and 37 IQ--and age-matched comparison participants (the TYP group), we found no differences in summary measures on an experimental risk-taking task. However, anxiety and IQ predicted risk-taking only in the ASD group. Risk-taking was correlated with behavioral inhibition in the ASD group and behavioral activation in the TYP group. We suggest that performance on the task was motivated by fear of failure in the ASD group and by sensitivity to reward in the TYP group. Behavioral markers of anxiety and cognitive ability may improve conceptualization of heterogeneity in ASD. (Contains 1 footnote, 4 tables, and 3 figures.)