The prevalence of lower urinary tract symptoms was determined in Korean men aged 50 and over. A community-based, epidemiologic study was performed in Yonchon County, Korea. The Korean version of the International Prostate Symptom Score (I-PSS) was used to assess the severity of urinary symptoms in a representative sample of 514 men. Nocturia and weak stream were the most prevalent symptoms and urgency was the least. Overall, 23.2% of the men were moderately to severely symptomatic: 17.7% in the age group of 50-59 years, 23.3% in that of 60-69 years and 35.3% in that of 70 years and over. The proportion of severely symptomatic men approximately doubled with each decade of age. The 'quality of life' score showed a high correlation with the I-PSS. Our estimation indicated that in 1995 approximately 800,000 Korean men had moderate to severe lower urinary tract symptoms that were likely to be associated with benign prostatic hyperplasia. The prevalence of moderate to severe lower urinary tract symptoms in Korean men is substantially similar to that in Caucasians.