PURPOSE: We investigated libido and sexual life satisfaction of middle-aged couples in Seoul. MATERIALS AND METHODS: A total of 2,034 couples ranging from 40 to 79 years old living in the Seoul metropolitan area were selected by stepwise random sampling. The questionnaires asking about erectile function, sexual performance, sexual life satisfaction, and libido were administered by trained interviewers. RESULTS: Interviews were completed for 1,356 couples(66.7%). The prevalence of severe and moderate loss of libido in the men was 29%. Decrease of libido correlated with increasing age. Higher scores on the erection scale of the O'Leary sexual function questionnaire were closely correlated with greater libido. In sexual function self-assessment, most male subjects did not complain of libido(53.8%), erection(61.7%), or ejaculation(63.8%) difficulties. Most couples(50.3% of the male and 53% of the female subjects) expressed satisfied with their sexual lives. Higher scores on the erection scale correlated with an increase in sexual satisfaction of both men and women. Fewer than half of the female subjects(40.4%) answered that they had 'no' or 'low' sexual interest. Younger age and more education were correlated with greater sexual interest. CONCLUSIONS: With increasing age, middle-aged couples living in Seoul showed a decrease in libido, sexual function, and sexual interest. However, satisfaction with their sexual life was high in general.