BACKGROUND: The aim of this study was to investigate the prevalence of obesity in Korean men with Klinefelter syndrome (KS) and the associated risk factors for obesity and hyperglycemia. METHODS: Data were collected retrospectively from medical records from 11 university hospitals in Korea between 1994 and 2014. Subjects aged >/=18 years with newly diagnosed KS were enrolled. The following parameters were recorded at baseline before treatment: chief complaint, height, weight, fasting glucose level, lipid panel, blood pressure, testosterone, luteinizing hormone, follicle-stimulating hormone, karyotyping patterns, and history of hypertension, diabetes, and dyslipidemia. RESULTS: Data were analyzed from 376 of 544 initially enrolled patients. The rate of the 47 XXY chromosomal pattern was 94.1%. The prevalence of obesity (body mass index >/=25 kg/m(2)) in Korean men with KS was 42.6%. The testosterone level was an independent risk factor for obesity and hyperglycemia. CONCLUSION: Obesity is common in Korean men with KS. Hypogonadism in patients with KS was associated with obesity and hyperglycemia.