Few studies have investigated methadone treatment of opiate dependent patients in primary health care settings. Using a prospective cohort design, the study investigated outcomes at 1 and 2 years for 240 patients treated by general practitioners (n = 79) or drug clinics (n = 161) at sites across England. Mean daily methadone dose for both groups was 50 mg. Reductions in illicit drug use, injecting, sharing injecting equipment, psychological and physical health problems, and crime, were found in both groups at follow-up. Patients treated in general practitioner (GP) settings reported less frequent benzodiazepine and stimulant use, and fewer psychological health problems at follow-up. Alcohol use outcomes were poor for both groups. Differences in treatment practices were found for GPs and clinics. Results show substantial reductions in a range of problems behaviours, among unselected samples of opiate dependent patients treated in GP and in clinic settings, which are sustained to 1-year and 2-year follow-up. (C) 2003 Elsevier Inc. All rights reserved.