BACKGROUND: Up to the present, there has been little study on chronic fatigue or chronic fatigue syndrome, and there is equally sparse relevant statistical data For this reason, we attempted to investigate the present status of fatigue, particularly its incidence and actual conditions. METHODS: The study subjects were 12,152 outpatients who visited family practice in hospitals all over Korea between July 24 and September 21, 1997. They were given a questionnaire which included questions reflecting the (U.S.) Center for Disease Control criteria defining chronic fatigue syndrome. RESULTS: Among the subjects, 861 people complained of fatigue in their response to the questionnaire and they became the focus of the study. Of this fatigue group, 426 people(49.4%) had rnanifested fatigue for more than 6 manths, and the male/female ratio was 54%/46%, respectively. People who re ported that fatigue impaired their ability to function on a daily basis made up 35.8% of the fatigue group and the percentage of people who had considered visiting a clinic duen to fatigue wasa unexpectedly high 52.8%. The reported causes of fatigue, in decreasing order, were. social interactio(mals 68.5%/ femals 45.1%); sleep disturbance(mals 26.8%/ femals 21.8%); and physical maladies(mals 24.2%/femals 26.5%). There were significant gender differences in social interaction relating to domestic problems(mals 4.7%/femals 16.7%) and emotional problems(mals 12.2%/femals 21.4%). Among 33 chronic fatigue syndrome patients who indicated what they thought were the causes of their problems, 68.8% reported physical maladies, 65.6% social life, 31.3% emotional problems, 21.9% sleep disturbance, and 21.9 % domestic problems. The associated symptoms of fatigue reported in both males and females, in decreasing order, included: myalgia, headache and neurologic symptoms. The prevalence of chronic fatigue was 0.27%. CONCLUSIONS: Our study showed that 7.1% of family practice outpatients complained of fatigue and that their daily activities or occupational life were disturbed as a result. This group demanstrates is serious need for medical assistance. Therefore, doctors should have more interest in fatigue, particularly in chronic fatigue syndrome, so as to provide real and versatile care.