The purpose of this longitudinal study was to examine the relationship between maternal depression and preschool children's mental health in a community sample. Cohort 1 (n = 97) consisted of mothers and children followed from 2 to 3 years of age. Cohort 2 (n = 97) consisted of mothers and children followed from 3 to 4 years of age. Mothers completed a self-report measure of depression twice during 1 year. The children's day care providers/nursery school teachers completed two instruments measuring the children's social competence and behavior problems at the end of the year. Maternal depression was significantly related to lower social competence and more behavior problems in the children. Although there were no significant mean differences in children's mental health scores by gender, boys of more depressed mothers were more likely to have poorer social competence and more behavior problems than girls. Item analyses suggest that the boys' behaviors may be particularly aversive for depressed mothers, increasing the likelihood that these mothers will respond to and reinforce their sons' difficult behaviors.