Drug Treatment Courts (DTCs) integrate therapeutic interventions for substance using offenders with the administration of justice. Available evidence indicates that DTCs are effective at reducing recidivism, but it is not yet established whether they are equally effective for all subgroups of offenders. The current study investigates the comparative effectiveness of a Canadian DTC among subgroups defined by ethnicity, gender, prior offending, and the presence of a co-occurring mental disorder. Results indicate greater reductions in recidivism among female and Aboriginal participants, and no differences in recidivism associated with the presence or absence of co-occurring mental disorders or the number of prior convictions. Longer duration of involvement with the DTC program was positively associated with reduced recidivism. The effectiveness of DTCs with distinct subpopulations may be related to their composition and inclusion of expertise relevant to the needs of diverse participants.