OBJECTIVE: Anticoagulant (AC) treatment in primary health care with regard to change over time, quality of care, and prevalence. DESIGN: Surveys of patients on AC treatment during 3 months in 1992 and 1997. SETTING: A community in the Stockholm metropolitan area. MAIN OUTCOME MEASURES: Main indications, rate of values within recommended treatment interval, prevalence. RESULTS: The number of patients increased in primary health care in the community from 115 in 1992 to 170 in 1997. There were no differences in age and sex distribution, nor in the main indications. Values within the recommended treatment range 10-25% at the community health centre (CHC) were 74% in 1992 versus 86% in 1997 (p