Diversion strategies aim to redirect drug-involved offenders away from the criminal justice system and into treatment. Despite the interest in diversionary practices, the emergence of an empirical evaluation literature has been slow. A methodological review of published outcome studies was conducted to investigate the current strength of evidence for the efficacy of diversion and aftercare practices for criminal offenders. Twenty outcome studies were identified for review: 19 on diversion and one on aftercare. The vast majority of studies were non-randomised evaluations, reflecting the paucity of rigorous evaluation work in this area. Although most studies were prospective, very few reported on long-term outcomes following treatment. Detail was lacking with regard to basic study characteristics, such as eligibility criteria and outcomes. Despite these methodological shortcomings, results provide some tentative evidence that diversion and aftercare programmes could be effective. Best practice elements of diversion and aftercare programmes are identified and feasible strategies to improve the methodological quality of future evaluations are considered.