Compared the impact on families of young children with externalizing behaviors (e.g., hyperactive, aggressive; n = 22), autism (n = 20), or no significant problem behaviors (n = 22) on several measures of family functioning. Previous studies have found heightened stress and parental maladjustment in families with externalizing children. The present study expanded upon that literature by (1) including a clinical control group to determine the specific impact of externalizing problems, (2) focusing on preschool aged children, and (3) using a new measure to directly ascertain parents' perception of impact. Compared to parents with normally developing children, parents with externalizing children reported more negative impact on social life, more negative and less positive feelings about parenting, and higher child-related stress. Moreover, parents of externalizing children reported levels of impact and stress as high as those reported by parents of children with autism. On broader measures of parental and marital well-being, however, the three groups of families of preschoolers did not differ. The implications of these findings for intervention are discussed.