The outcomes of a structured warfarin patient education programme were compared with those of an unstructured programme. For both programmes, knowledge and satisfaction levels were determined, incidence of complications of warfarin therapy were noted, and prothrombin time results were examined. The 23 patients who participated in the structured educational programme were selected from among vascular surgery patients. The comparison group was composed of 10 patients who had mechanical prosthetic valves inserted. The structured programme was designed for the study, and implemented by staff nurses. The comparison group received the usual unstructured educational programme. Post-treatment assessments were made before discharge and at 1 month and 3 months after discharge. Interview guides were developed, to determine knowledge and satisfaction. At the predischarge interview, significant differences between the treatment and comparison groups were observed related to knowledge of elements of warfarin therapy. The most important effects of the programme related to specific instructions to promote safety. The interviews 1 month and 3 months after discharge demonstrated that knowledge changed in several areas for both groups. Overall, both groups were satisfied with the information they received. The majority in both groups did not experience complications. Prothrombin times were available for some patients. Those obtained indicated that prothrombin times were not consistently within the therapeutic range for 60% of the time or more. The study supports the use of a structured educational programme as one element in achieving safe, effective warfarin therapy. Reasons for changes in knowledge over time merit further exploration, as does the relationship between optimal control of therapy and educational programmes.