The histopathologic features of 855 cervical biopsies were correlated with the presence of human papillomavirus DNA using in situ hybridization (ISH) with biotin labeled type specific probes for Human Papilloma Virus (HPV) types 6, 11, 16, 18, 31, 33 and 51. HPV-DNA was found in 18% (13/72) of cervical intraepithelial neoplasia I (CIN I), 30% (35/115) of CIN II, 28% (57(206) of CIN III, in 84% (21/25) of flat condyloma and in 13% (15/112) of normal cervical tissue. HPV DNA was detectable in 11% (5/46) of cervical adenocarcinoma and in 21% (59/279) of squamous cell carcinoma (SCC) of the cervix. High risk HPV types were identified more often than low risk HPV types in CIN I, CIN II, CIN III and SCC. HPV type 16/18 predominates over HPV types 31/33/51 in CIN I, flat condyloma and in SCC. The prevalence of HPV was strongly associated with the grade of differentiation of SCC. It was identified in 59% (23/39) of well differentiated SCC, in 18% (25/142) of moderately differentiated and in 11% (11/98) of poorly differentiated SCC.