Objective: Service use trends showing increased off-label prescribing in very young children and reduced psychotherapy use raise concerns about quality of care for early disruptive behavior problems. Meta-analysis can empirically clarify best practices and guide clinical decision making by providing a quantitative synthesis of a body of literature, identifying the magnitude of overall effects across studies, and determining systematic factors associated with effect variations. Method: We used random-effects meta-analytic procedures to empirically evaluate the overall effect of psychosocial treatments on early disruptive behavior problems, as well as potential moderators of treatment response. Thirty-six controlled trials, evaluating 3,042 children, met selection criteria (mean sample age, 4.7 years; 72.0% male; 33.1% minority youth). Results: Psychosocial treatments collectively demonstrated a large and sustained effect on early disruptive behavior problems (Hedges' g = 0.82), with the largest effects associated with behavioral treatments (Hedges' g = 0.88), samples with higher proportions of older and male youth, and comparisons against treatment as usual (Hedges' g = 1.17). Across trials, effects were largest for general externalizing problems (Hedges' g = 0.90) and problems of oppositionality and noncompliance (Hedges' g = 0.76), and were weakest, relatively speaking, for problems of impulsivity and hyperactivity (Hedges' g = 0.61). Conclusions: In the absence of controlled trials evaluating psychotropic interventions, findings provide robust quantitative support that psychosocial treatments should constitute first-line treatment for early disruptive behavior problems. Against a backdrop of concerning trends in the availability and use of supported interventions, findings underscore the urgency of improving dissemination efforts for supported psychosocial treatment options, and removing systematic barriers to psychosocial care for affected youth. (Contains 2 figures and 2 tables.)