Maternal ratings of anxiety, depression, and irritability were analyzed in 1390 children (6-16 years of age), including 233 children with high functioning autism (HFA, IQ greater than or equal to 80), 117 children with low functioning autism (LFA, IQ less than 80), 187 typical children, and 853 children with other disorders. As a group, children with HFA were characterized as irritable and anxious, and children with LFA and ADHD-combined type were irritable only. Children with anxiety disorders were anxious only. Children with major depression or dysthymic disorder were depressed and irritable. Elevated levels of irritability, anxiety, or depression were not found in ADHD-inattentive type, mental retardation, brain injury, or typical development. The frequency of parent reported anxiety symptoms was similar for children with an anxiety disorder and HFA, though some symptoms were more severe in children with anxiety disorders. Children with depression had more frequent and more severe depressive symptoms than children with HFA. Mothers of 54% of children with HFA and 42% with LFA reported depressed mood in their children. Percentages were higher for anxiety (79% and 67%) and irritability (88% and 84%). These remarkably high percentages justify routinely assessing all children with autism for depression, anxiety, and irritability. (Contains 6 tables.)