About 10.97% of women with children aged 1 to 4 years old are identified with depression. Children of mothers with depression are more likely to exhibit externalizing behavior problems, and these problems have been reported to appear more frequently in male children. We examined the association between maternal depression and externalizing behavior in toddlers, and whether child sex moderated these effects, as previous studies have shown child behavior to be linked to both child sex and maternal depression. The sample included 186 mother/child dyads (95 male children) who were recruited in the first trimester of pregnancy from an urban hospital. We measured maternal depression using the Beck Depression Inventory-II at 24 months of child age. Mothers were identified as having high or low levels of depression based on the clinical cutoff score of 17 or higher. Externalizing behavior was measured at 36 months of child age using maternal reports on the Child Behavior Checklist (CBCL). The raw scores on the CBCL were then converted into t-scores and used in analyses. We used univariate analysis of variance to examine differences in externalizing behavior, with high vs. low levels of maternal depression and child sex as the independent variables and scores on the externalizing behavior subscale as the dependent variable. There was a significant association between maternal depression at 24 months and externalizing problems at 36 months (F=201.344, p=0.045). Mothers at or above clinical cut-off for depression at 24 months of child age later reported higher externalizing problems in their child at 36 months of child age. There was no main effect of child sex, or an interaction of child sex and maternal depression. Thus, this association was not different for boys and girls. These results suggest mothers who have clinical levels of depression at toddler age have children with higher maternal reports of externalizing problems at preschool age. This association did not vary as a function of child sex. This result contradicts the expected result that externalizing behaviors in male toddlers would be more severe than in female toddlers. One implication is that treating maternal depression during early childhood may decrease the prevalence of externalizing behaviors in children. This may lead to healthier social development of these children