OBJECTIVE: Our purpose is to conduct an epidemiological study of chronic fatigue syndrome (CFS) and its syndrome types and symptoms of traditional Chinese medicine (TCM) among adults (20-50 years old) in Hong Kong, and to discuss the TCM pathogenesis. METHODS: Design: Cross-sectional questionnaire survey. Measures: Demographic data, CDC (1994) CFS diagnostic criteria, Trudie Chalder fatigue scale, and China national standard for TCM syndrome types criteria. Subjects: Twenty to fifty years old adults by convenient sampling. RESULTS: One thousand and thirteen subjects were successfully interviewed. Five hundred and eighty-five subjects (57.8%) had different levels of fatigue. Sixty-five subjects (6.4%) met CFS diagnostic criteria. In terms of TCM syndrome types, blood stasis due to qi deficiency had the highest prevalence (35.7%) among CFS. In the 54 symptoms investigated in total, the first eight symptoms in order of appearing rates were soreness of loins and weakness in knees, poor spirit, lassitude, pain, insomnia, forgetting, vessels blood stasis, vertigo and dazzle. The mostly appeared tongue figures were pale and corpulent or pale dim tongue proper, white and white greasy tongue coating, and the mostly appeared pulse figure was sunken-thin. CONCLUSION: The point prevalence of CFS among adults of 20 to 50 years old was found to be 6.4%. The most prevalent TCM syndrome type was blood stasis due to qi deficiency. The TCM pathogenesis of CFS was deficiency of origin, mainly deficiency of qi and kidney, with excess of superficiality.