We assessed the association between different HPV genotypes, HIV infection, and cervical squamous intra-epithelial lesions (SIL) in 236 women with known HIV serostatus enrolled in a longitudinal multicentric study in Italy. Of these women, 135 were HIV-infected, and were not markedly different from HIV-negative women with regard to demographic characteristics, sexual practices, smoking, or intravenous drug use. We obtained 232 cervical smears suitable for cytological examination and HPV-genotype analysis (134 from HIV-positive women and 98 from HIV-negative women). For 86 HIV-positive and 89 HIV-negative women, the smears appeared normal at cytomorphological analysis. Cytological dysplasia of varying degrees was detected in 48 smears from HIV-positive women and in 9 from HIV-negative women. HPV prevalence, assessed using polymerase-chain-reaction analysis, did not significantly differ between HIV-positive and HIV-negative women. The prevalence of HPV-associated SIL was much greater among HIV-infected women. The most frequently detected genotypes in both groups were HPV 16 and HPV 18. The prevalence of HPV 16 among HIV-positive women was similar to that for HIV-negative women; this was also true for HPV 18. However, in the HIV-positive group, most of these genotypes were associated with SIL. HIV-positive women showed a wider spectrum of genotypes, including non-oncogenic and rare types. An association between SIL and HIV infection was confirmed for all HPV genotype classes.