Chronic Fatigue Syndrome in Korea 2.5% reported by researches in Western countries and the difference is thought to have resulted from racial difference. According to the report of a research on patients at a certain region in the U.S., prevalence of CFS was 1.0% among whites, 2.75% among blacks and 0.12% among Asians (15). And a Japanese study from a nationwide survey reported the preva- lence of CFS was 0.85 per 100,000 persons during 1992 (16). As for the difference of CFS prevalence between our study and the Japanese study, it should be noted that the diagnos- tic criteria of CFS in the Japanese study was based on CDC in 1988 and the study subjects were general population. Patients with explained CF were 80.5% of CF cases, and psychosocial causes (57.1%) were more frequent than physi- cal causes (42.9%). The most common cause was stress, fol- lowed by depression, adjustment disorder, diabetes (uncon- trolled), asthma, anxiety disorder, etc. In several researches in Western countries, the major causes of CF were reported to be psychological disorders, and the result of our study is consistent with that of the previous study in Korea (7, 17, 18). Thus, it is considered that stress is the major cause of CF and psychosocial causes are more frequent than physical ones in Korea. Subjects classified as prolonged fatigue and CF tended to be older, without a spouse, and have higher educational quali- fication compared to those classified as no fatigue. Although several researchers reported that fatigue has no age predilec- tion, it was reported that fatigue is more common in adults than in children and adolescents and its frequency increases with age from middle age to older ages (19, 20). In addition, it was reported that fatigue is inversely proportional to eco- nomic level and the intensity of fatigue is lowest in the high- est socio-economic class (21, 22). These results may be due to the different perception of fatigue, which is a subjective symptom, but further epidemiological research is needed in Korea. We compared CFS with the other three groups of CF in order to identify their socio-demographic and clinical char- acteristics, but it was difficult to delineate clinical character- istics of CFS because the number of subjects with CFS (10 patients) in our study was too small. In addition, there were no socio-demographic characteristics that showed a signifi- cant difference compared to the other three groups. Howev- er, among the eight other symptoms of the CFS diagnostic criteria except fatigue, the tenderness of cervical or axillary lymph node (60%), multi-joint pain without arthritis (80%), and muscle pain (90%) showed higher frequencies in the CFS group than in the other three CF groups (although the dif- ference was not significant with the ICF group). Since the eight symptoms are included in the diagnostic criteria for CFS, it seems natural that their frequencies are higher in the group of CFS than in explained CF. And due to the bias of this univariate analysis, it was not conclusive whether these symptoms were distinct in CFS from explained CF. However, these symptoms are known to be related to infection resulting 533 from abnormal immune function, so this result may provide a clue to the opinion that CFS is related to infection or immu- nity. Several researches have shown that many flu-like symp- toms observed in CFS patients are caused by an immune dis- order (23, 24). Previous researches have demonstrated that CFS is frequent- ly accompanied with emotional disorders such as depression and anxiety (25, 26). And according to the result of a meta- analysis on medically unexplained physical symptoms and depression and anxiety, CFS had a higher frequency of depres- sion than irritable bowel syndrome and a higher frequency of anxiety than fibromyalgia (27). In this study as well, 80% of CFS showed depression. The limitations of this study are as follows: since the sub- jects of this study were patients visiting community-based primary care clinics, their point prevalence of CF and CFS may not represent those of the general population. And the population distribution of the patients who visited the eight primary clinics participated in this study might not be con- sistent with the one from the entire community-based pri- mary care in Korea. In addition, because both the previous study in Korea and the present study focused on patients visit- ing medical care institutions, future studies on the general population in Korea may report a lower prevalence of CF and CFS. The second limitation is the possibility that the deci- sions made by physicians in the eight community-based pri- mary care clinics to investigate the cause of CF might not have been completely consistent although they analyzed the cause of CF based on objective criteria. The third limitation is related to the number of subjects. In order to estimate the prevalence of a rare disease like CFS, a larger number of sub- jects are required. If the number of subjects is not big enough, the prevalence may be underestimated or overestimated. Last- ly, not all patients during the study period were included in the study. Among the 1,962 patients who visited medical care institutions during the study period, 15% (314 persons) were excluded from the study. If they were included in the analysis, the point prevalence of CF and CFS was likely to be different. However, no statistical difference was found in terms of age and sex between the 314 non-participants and 1,648 participants. Despite these limitations, this study is meaningful in that it is the first study on patients visiting one of eight commu- nity-based primary care in Korea to investigate the point pre- valence of CF and CFS. The results of this study are expected to be utilized in future epidemiological research on CF and CFS in the general population in Korea. ACKNOWLEDGEMENTS We thank Dr. Haeng Lee, Dr. Soo Young Kim, Dr. Eu Yeol Yun, Jin Ha Kim, Hyo Ee Jun, Hyun Jun Cha, So Hyun Lee, Eun Young Choi, Byong Mo Kim for their efforts to collect