A case of squamous-cell carcinoma arising in association with perianal condyloma acuminatum was studied by light microscopy. The eight previously reported cases of malignant transformation of perianal and anorectal condylomata acuminatum are reviewed and the salient features described. Light microscopic examination of the case reported here demonstrated several foci of subtle and abrupt transition from condyloma acuminatum to epithelial dysplasia and to carcinoma in situ with focal frank invasion. This study further substantiates the existence of malignant transformation of condyloma acuminatum, particularly in perianal skin.