The purpose of this study was to investigate the importance of enjoyment of exercise in a health care-based intervention aimed at promoting physical exercise in primary health care patients. In a controlled study design, the intervention group was offered a wide range of group exercises over 3 months, followed by support in designing their own exercise program. The control group received usual care. Enjoyment of exercise and exercise level were measured. Associations between enjoyment and exercise level were analyzed using Spearman's rank correlation coefficients. Changes in enjoyment between and within study groups were analyzed by the independent and paired t-test. Associations were found between enjoyment and exercise level (r=0.36, P<0.01), as well as between changes in enjoyment and changes in exercise level (r=0.34, P<0.01). At the 12-month follow-up, enjoyment of exercise was 25% higher in the intervention group than in the control group (P<0.01). In this group of primary health care patients, enjoyment of exercise was associated with exercise level. Enjoyment of exercise seems to be a mediator of exercise level. Furthermore, health care-based interventions seem to be able to affect enjoyment of exercise. Enjoyment of exercise may be important for the long-term effectiveness, of health care-based interventions.