Background: Violent trauma is common in urban communities. We explored the hypothesis that past trauma could moderate the effect of a cognitive behavioral intervention designed to prevent depression among urban, low-income mothers. Methods: Synthesis of two pilot randomized trials of problem solving education (PSE) among 93 mothers of children hospitalized in the neonatal intensive care unit or enrolled in community-based Early Intervention programs. Outcomes included depressive symptoms, perceived stress, and social functioning. Results were adjusted for baseline depressive symptoms, then stratified according to subjects' trauma history. Results: Fifteen of the 44 PSE subjects (34%) experienced a moderately severe depressive symptom episode during the 3-month follow-up period, as opposed to 21 of 45 control subjects (47%), for a nearly significant adjusted odds ratio (aOR) of 0.36 (95% CI: 0.13, 1.02). Among mothers without trauma histories, far fewer PSE mothers (5 of 24; 21%) experienced an episode of moderately severe depressive symptoms than control mothers (12 of 26; 46%) for a significant aOR of 0.15 (95% CI: 0.03, 0.79). Conversely, among mothers with trauma histories, a similar proportion of PSE mothers (10 of 19; 53%) experienced an episode of moderately severe depressive symptoms as control mothers (9 of 19; 47%). Similar trends held for perceived stress and social functioning. Conclusions: PSE may be more effective at preventing depression among mothers without trauma histories. Our results are consistent with the depression treatment literature, but are novel because they support the principle of intervention moderation in risk prevention, as opposed to treatment, paradigm. Depression and Anxiety, 2011. © 2011 Wiley-Liss, Inc.