CONTEXT: Despite their important influence on child health, it is assumed that fathers are less likely than mothers to participate in pediatric obesity treatment and prevention research. OBJECTIVE: This review investigated the involvement of fathers in obesity treatment and prevention programs targeting children and adolescents (0-18 years). DATA SOURCES: A systematic review of English, peer-reviewed articles across 7 databases. Retrieved records included at least 1 search term from 2 groups: "participants" (eg, child*, parent*) and "outcomes": (eg, obes*, diet*). STUDY SELECTION: Randomized controlled trials (RCTs) assessing behavioral interventions to prevent or treat obesity in pediatric samples were eligible. Parents must have "actively participated" in the study. DATA EXTRACTION: Two authors independently extracted data using a predefined template. RESULTS: The search retrieved 213 eligible RCTs. Of the RCTs that limited participation to 1 parent only (n = 80), fathers represented only 6% of parents. In RCTs in which participation was open to both parents (n = 133), 92% did not report objective data on father involvement. No study characteristics moderated the level of father involvement, with fathers underrepresented across all study types. Only 4 studies (2%) suggested that a lack of fathers was a possible limitation. Two studies (1%) reported explicit attempts to increase father involvement. LIMITATIONS: The review was limited to RCTs published in English peer-reviewed journals over a 10-year period. CONCLUSIONS: Existing pediatric obesity treatment or prevention programs with parent involvement have not engaged fathers. Innovative strategies are needed to make participation more accessible and engaging for fathers.