Mental health is an important contributor to child and family well-being. Conversely, mental illness is a well-recognized risk factor for child maltreatment and repeated involvement with child welfare systems. Presently little is known about how primary and secondary maltreatment prevention programs conceptualize mental health, or if changes to mental health are observed across maltreatment prevention studies. To address this gap in knowledge the current study systematically reviewed twenty years of research to identify and describe the mental health outcomes of caregivers and children who were enrolled in primary or secondary maltreatment prevention outcome studies. Studies were eligible for inclusion if the prevention focused on the general population or families exhibiting early risk factors for maltreatment, employed a randomized controlled trial design, included at least one measure of mental health, contained at least one prospective outcome measure of child maltreatment, and was published in English-language in or after the year 2000. A systematic search of MEDLINE, PsycINFO, Embase, Scopus, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, Campbell Library of Systematic Reviews, California Evidence-Based Clearinghouse for Child Welfare (CEBC), Child Welfare Information Gateway, and Social Care Online identified 931 studies, thirty-three of which met the inclusion criteria. Fourteen dimensions of mental health were identified across included studies. Measures of mental illness (n = 95) appeared roughly seven times more often than measures of mental well-being (n = 13). Studies reported treatment group improvements to mental health and maltreatment prevention (n = 10), improvements to mental health but not maltreatment prevention (n = 8), improvements to maltreatment prevention but not mental health (n = 5), or neither improvements to mental health nor maltreatment prevention (n = 10). Across programs reporting changes to mental health, the most commonly reported improvements were to child behavior (n = 8) and parenting stress (n = 6). Results indicate primary and secondary prevention programs more often improve mental health than prevent child maltreatment. Future studies aimed at strengthening the efficacy of child maltreatment prevention in community settings should consider targeting additional indicators of mental health that are commonly encountered in community settings, and strengthen measures of child maltreatment to more frequently include multiple indicators and multiple sources. Future studies should also examine the interaction of socioeconomic and structural contributors to mental health and child maltreatment prevention.