This study examined the masturbatory experiences and other sexual activities of young Korean males in military service. The actual status of masturbation and its relationship to sexual activity questionnaire. A total of 1,212 young males among military personnel in Korea were interviewed with sexuality questionnaires on masturbation, sexual intercourse and personal characteristics. We divided these subjects into four groups according to the age of initiation of masturbation and analyzed the relationship between masturbation and other sexual activities. The mean age of subjects was 22.03 ± 1.22 (19-27) years. The percentage of men who reported ever having masturbated was 98.1% (1189/1212) and the average age of initiation of masturbation was 14.26 ± 1.66 years. So we divided 1,212 males into four groups on the basis of the average age below and above one standard deviation. Overall, 67.7% (821/1212) had experienced sexual intercourse, and significantly, the earlier the initiation age of masturbation, the higher the coitus rate in each group (p < 0.05). About 21.5% of the men who were not virgins had experienced their first sexual intercourse with prostitutes. The mean age of first coitus, the incidence of sexually transmitted disease (STD) and the frequency of masturbation were closely linked to the initiation age of masturbation, respectively (p < 0.05). A masturbatory guilt feeling was seen in about 10.9% (132/1212) and there was no significant difference according to the types of religious worship (p = 0.227). On the basis of this study, sexual activities generally increased accordingly as the beginning of masturbation was earlier. Coital incidence in this study was 67.7% for young males in Korean military service, and 21.5% of them had their first sexual intercourse with prostitutes. Prostitution still plays an important role in the sexual lives of males in Korea. The incidence of STD was over 10% and homosexual manifestation was seen in 1.07% of subjects. Thus a proper and sound sex education at school during childhood is needed in Korea. A large scale survey of sexual behavior in various populations is essential for the improvement of correct sexual concepts.