The frequency, course, and inter-relationships of atypical eating, sleeping, self-injurious behavior, aggression and temper tantrums in children with autism and children with a history of language impairment (HLI), was investigated using a parent interview that was created to examine these problem behaviors. The relationships between these behaviors and language, IQ, severity of autistic symptoms and depression were also assessed. Atypical eating behavior, abnormal sleep patterns, temper tantrums, and self-injurious behavior were significantly more common in the children with autism than those with HLI. Within the autism group, children who exhibited more atypical behaviors tended to have a lower nonverbal IQ, lower levels of expressive language, more severe social deficits and more repetitive behaviors. No relationship between the number of atypical behaviors and measures of cognitive or language ability was noted in the HLI group. However, having more atypical behaviors was related to increased restricted, repetitive behaviors in children with HLI. The atypical behaviors could be divided into two groups: abnormal eating and sleeping, which were independent and tended to begin early in life; and self-injury, tantrums and aggression, which began later and were inter-related. Sleep abnormalities were more common in children (groups combined) diagnosed with major depression.