Cervical cancer is the second most common cancer in women worldwide and the leading cause of cancer deaths in Tanzanian women. Prevention of cervical cancer relies on the detection and treatment of Squamous Intraepithelial Lesion (SIL), a premalignant disease stage. Worldwide there are overwhelming reports associating SIL and HIV infection, however in Tanzania such reports are limited. A cross-sectional hospital-based descriptive study was conducted to determine the prevalence and severity of SIL in 234 HIV seropositive and seronegative women aged 18-68 years old at Kilimanjaro Christian Medical Centre in northern Tanzania. A structured questionnaire was used to collect sociodemographic data. In addition, blood was collected for rapid HIV antibody testing and CD4+ T-lymphocyte counts to associate with prevalence and severity of SIL from the cervical smear collections. A total of 214 subjects had smear results regarded as valid for interpretation, of which 46.3% were HIV seropositive. Overall rate of SIL was 17%. Proportion of SIL among HIV seropositive subjects was 32% versus 4% in seronegative subjects (OR=13.3, 95% CI=4.2-46.4). Low CD4+ Tlymphocyte cell count was associated with higher prevalence of SIL (P=0.001). The relationship between CD4+ T-lymphocyte cell counts and the severity of cervical SIL was significant (P=0.007). Marital status and number of lifetime sex partners were risk factors significantly associated with SIL (P=0.004 and 0.005, respectively). SIL was not associated with age, education level, parity or age at sex debut. The prevalence and severity of cervical SIL was significantly associated with HIV infection and immunologic disease progression. These findings underscore the need for HIV screening among women with SIL, and the need for cervical cancer screening in HIV-infected women. Marital status and number of lifetime sex partners were significant risk factors associated with SIL. _______________________________________________________________________________________