This study examines potential improvement in treatment adherence during a study of involuntary outpatient commitment among individuals with severe mental illnesses. Involuntarily hospitalized subjects, awaiting discharge under outpatient commitment, were randomly assigned to be released or continue under outpatient commitment after hospital discharge. A nonrandomized group with a recent history of serious violence was also studied under outpatient commitment. Randomized control and outpatient commitment groups did not differ significantly in group comparisons of treatment adherence. However, analyses of all subjects, including nonrandomized violent subjects, showed that those who underwent sustained periods of outpatient commitment (6 months or more) were significantly more likely to remain adherent with medication and other treatment, compared with those who underwent only brief outpatient commitment or none. Administration of depot antipsychotics also significantly improved treatment adherence independently of the effect of sustained outpatient commitment. Sustained periods of outpatient commitment may significantly improve adherence with community-based mental health treatment for persons with severe mental illness and thus may help improve other clinical outcomes affected by adherence.