Bipolar (BD) symptomatology is prevalent in children with autism spectrum disorders (ASD) and may lead to increased impairment. The current study compared clinical and neurocognitive impairment in children (7-13 years) diagnosed with ASD (n=55), BD (n=34), ASD + BD (n=23), and a non-clinical control group (n=27). Relative to the ASD group, the ASD + BD group reported elevated rates of aggression and delinquency, behavioral disorders, depression, obsessive-compulsive disorder, and suicidal ideation, and poorer performance on the Stroop Color-Word Test. Future research might address how best to improve diagnostic assessment and adapt treatment to meet the needs of this uniquely impaired population. (Contains 5 tables.)