Introduction: Metabolic syndrome is an emerging clinical problem in psychiatric patients. However, it is uncertain that what is different between psychiatric and non-psychiatric patients. Methods: We performed analysis in a chronic psychiatric hospital and enrolled 225 patients who admitted from 2005 to 2006. The prevalence of metabolic syndrome was assessed based on the ATP-III with the new criterion of waist circumference in the Asia-Pacific Region. Drugs medicated longer than three months were investigated. Results: The study population was relatively young (41.1짹8.8 years) and obese (waist in men; 91.3짹9.2 cm, waist in women; 84.1짹8.8 cm). 60% of patients met waist criterion of metabolic syndrome and 56% of patients met low high density lipoprotein criterion. Mean serum triglyceride was high (170.0짹119.7 mg/dL) and 46% of patients met high triglyceride criterion. However, less than 10% of patients showed impaired fasting glucose or high blood pressure (5%, 9%, respectively). The overall prevalence of metabolic syndrome was 34.2% by applying ATP- III criteria (40% in men and 20% in women respectively). No specific anti-psychotic drugs were related to significant increase in metabolic syndrome incidence. Conclusion: The prevalence of metabolic syndrome in psychiatric patients was high considering their young age. Feature characteristics were abdominal obesity, hypertriglyceridemia, and low HDL rather than hypertension or impaired fasting glucose. The active screening and early intervention of these metabolic derangements should be warranted.