Objective: This study aimed to improve the sexual health of Korean elderly people and to prepare adequate education programs by investigating their sexual behavior. Design and Method: From September to November 2013, we surveyed elderly people in senior welfare centers or public parks. Participants filled out a selfadministered questionnaire, which elicited information concerning: demographic information, information on their sexual behavior, purchase of sexual services, experience of STIs, and experience of sex education. Results: A total of 403 men participated in the study. The number of sexual partners was higher in blue-collar workers than in men with other occupations, in men with a spouse than those without one. Of the respondents, 15.9% had had a sexual experience with a prostitute (client group). The proportion of people with a spouse, of a lower age, of middle socioeconomic status, and blue-collar workers was higher in the client group. The prevalence of STIs based on this study was 6.0% and 83% of the people with STIs sought medical treatment. Of the STIs, 57.3% were transmitted from a casual sex partner, the prevalence of which was higher in the client group than in the non-client group (18.8% vs. 3.5%). Only 8% of the respondents had received sex education in the past year. The most desired education topics were symptoms of STIs (37.7%), followed by sexual conflicts after middle age (33.7%), and treatment of erectile dysfunction (22.3%). Conclusions: Elderly people are a new group vulnerable to STIs. To control these infections, powerful policies containing sex education and medical services will be needed.