PURPOSE: The aim of this study was to evaluate the prevalence of lower urinary tract symptoms (LUTS) among Korean men aged > or =40 years. METHODS: We performed a population-based, cross-sectional door-to-door survey on a geographically stratified random sample of men aged > or =40 years. All respondents were asked about the presence of individual LUTS using a questionnaire based on 2002 International Continence Society definitions. For comparison, we also defined nocturia as two or more nocturnal micturitions per night. The International Prostate Symptom Score (IPSS) questionnaire was used to assess LUTS severity. RESULTS: Responses from 1,842 subjects were analyzed. The overall prevalence of LUTS was 83.4%. Storage LUTS (70.1%) were more prevalent than voiding (60.4%) or postmicturition LUTS (38.3%). When nocturia was defined as two or more nocturnal micturitions per night, voiding symptoms became most prevalent (storage, 39.7%; voiding, 60.4%; and postmicturition, 38.3%). More than 90% of our population described the severity of their urinary symptoms as moderate (8-19) or severe (20-35). The prevalence and severity of LUTS increased with age. CONCLUSIONS: LUTS are highly prevalent among Korean men, and its prevalence increases with age. Increased public awareness and a larger number of treatment options are needed to appropriately manage symptoms and their consequences.