Study objectives: To compare treatment completion rates at 8 and 12 months after treatment initiation for patients with active TB treated with either directly observed therapy (DOT) or self-administered therapy (SAT). Design: Retrospective comparison study of DOT and SAT concurrent patient cohorts. Setting: Urban Tuberculosis Control Program within a Department of Public Health. Patients: Three hundred nineteen patients confirmed to have active TB between July 1, 1994, and June 30, 1995, who began outpatient drug therapy. Interventions: Patients and/or their physicians chose to receive their anti-TB drug therapy by DOT (n=113) or SAT (n=206) and were assessed for treatment completion at prospectively determined times, 8 and 12 months. Measurements and results: Proportions of patients who completed treatment at 8 and 12 months without crossing over to the other group were compared. At 8 months, 52% of DOT and 35% of SAT patients had completed treatment (relative superiority of DOT, 49%; p=0.003). At 12 months, completion rates were 70% for DOT patients and 53% for SAT patients (relative superiority of DOT, 30%; p=0.006). Conclusions: In our setting, patients receiving DOT were much more likely to complete treatment earlier than those receiving SAT. Even with DOT, only 52% of patients had completed treatment by 8 months.