To determine whether neoplastic cervical lesions in women are associated with papillomavirus infections in their sexual partners, we used a colposcope to examine male sexual partners of women with cervical flat condyloma (294 cases) or cervical intraepithelial neoplasia (186 cases), before and after 5 percent acetic acid was applied to the penis and the anogenital area. Condylomata acuminata, papules, and macules were observed in 309 of the 480 men (64.4 percent). In 204 of them (42.5 percent), macules or slightly elevated papules were detected only after application of acetic acid. Condylomata acuminata or lesions showing histologic features of condyloma were found in 121 partners (41.2 percent) of women with condyloma, but in only 10 partners (5.4 percent) of women with cervical intraepithelial neoplasia. Penile lesions showing histologic features of intraepithelial neoplasia were found in 61 partners (32.8 percent) of women with cervical intraepithelial neoplasia, but in only 4 partners (1.4 percent) of women with flat condyloma. Thirty-six (60 percent) of the 60 macules or papules tested contained papillomavirus DNA sequences. Human papillomavirus types 16 and 33 were almost exclusively found in penile intraepithelial neoplasia. Type 6, type 11, and the recently recognized type 42 were found in lesions showing features of condyloma or minimal histologic changes. As yet uncharacterized papillomaviruses were found in 15 percent of the specimens. These data support the concept that cervical carcinomas and precancerous lesions in women may be associated with genital papillomavirus infection in their male sexual partners.