Purpose: Although concern about the health disorders in aging men have been growing, the association has not been elucidated in relation to the late onset male hypogonadism(LOH) and metabolic syndrome(MS). In this background, we evaluated the clinical impact of MS on LOH symptoms and serum total testosterone level. Materials and Methods: 100 patients with LOH symptoms who visited to the urology clinic between May, 2004 and October, 2006 were analyzed. Of all object, 48 patients were associated with MS(Group I) and 52 patients were not(Group II), based on the NCEP-ATP III(2001) guidelines. We compared the LOH status with Saint Louis University Androgen Deficiency in Aging Males(ADAM) questionnaire, serum total testosterone level, as well as prevalence of MS components between the two groups. Results: The overall prevalence of MS was 48% among LOH patients. The average age of group I and II were 57.7+/-10.5 and 58.6+/-11.2 years, respectively. Positivity for ADAM questionnaire was 83.3% in group I and 76.9% in group II, respectively(p<0.05). Serum total testosterone level decreased according to number of components of MS(p<0.05). The obesity group had significantly decreased serum total testosterone level(3.41+/-1.34 ng/ml) comparing to control group(4.41+/-2.23 ng/ml)(p<0.05). Conclusions: MS and its risk factors were significantly associated with LOH symptoms and positively correlated with the severity of disease. The evaluation of MS are required for the diagnosis and treatment of the patients with LOH.