Physical work load was assessed by doctors and patients to have contributed to the health problems leading to sickness certification in 48.4% of 1413 patients certified sick by 118 general practitioners in Buskerud county, Norway (1986). Correspondingly, psychological factors were considered contributory in 32.1%. The potential for prevention of health problems underlying sickness certificates was reported in 37.1%. As expected, the frequency of sickness certification in which physical work load and psychological factors were considered to have contributed varied with the patients' occupation, type of work, and health problem. Physical work load was assessed as contributory particularly in patients with musculoskeletal/connective tissue diseases whose work involved much walking and lifting (93.2%) or was physically strenuous (94.0%). Psychological factors were assessed as contributory in a high percentage of cases whose work was mostly sedentary. The findings indicate that the potentials for prevention as assessed by doctors and patients were highest when the health problems underlying sickness certification were associated with musculoskeletal/connective tissue diseases. The results indicate a potential for prevention and limitation of sickness certification which may be utilized by a better collaboration between community medicine and occupational health services.