To investigate the role of men in cervical cancer, 816 husbands of women enrolled in four case-control studies of cervical neoplasia in populations at high (Colombia) and low (Spain) risk for cervical cancer were interviewed. Exfoliated cells from the penis were obtained and analyzed by polymerase chain reaction for the presence of human papillomavirus (HPV) DNA. Penile HPV DNA prevalences were higher in husbands of women with cervical neoplasia than in husbands of controls. Husbands of controls in Colombia had a 5-fold higher penile HPV DNA prevalence than the corresponding husbands in Spain. Strong dose-response relationships were found between penile HPV DNA prevalence and all sexual behavior-related variables in Spain but not in Colombia. Sexual promiscuity is the most important risk factor for penile HPV infections. Differences in HPV DNA prevalence in the male populations of Spain and Colombia are consistent with their 8-fold difference in cervical cancer incidences.