Background: Both human immunodeficiency virus (HIV) and hepatitis B virus (HBV) infection are highly prevalent in sub-Saharan Africa, and co-infection is likely to occur. Co-infection raises several challenges: there are changes to the natural history of HBV infection, resistance may emerge in HBV as a result of HIV treatment, and changes should be made to the treatment regimens to take both infections into account. Epidemiological data on this problem is therefore needed.Methods: This study was conducted in Haydom hospital in rural Tanzania. The HIV Care and Treatment Clinic (CTC) at this hospital provides free HIV treatment according to national Tanzanian guidelines. The patients included in the study were HIV infected attending this clinic. 120 patients were tested for HBV infection and evidence of previous HBV exposure, using a five parameter HBV rapid test (OnSite HBV 5-Parameter Rapid Test). The parameters used were HBsAg, HBeAg, anti-HBs, anti-HBc and anti-HBe. Patient files were studied for information about HIV treatment and most recent lab results, including CD4, platelets and ALT. The association between lab results and HBV infection was calculated using a two sample independent t-test.Results: 11 (9%) of the 120 participants tested positive for HBsAg, as a marker of HBV infection. 47 (39 %) patients showed serological evidence of HBV exposure. 62 (52 %) patients tested negative for all parameters. There were no significant difference in ALT, platelets and CD4 between HBsAg-positives and HBsAg-negatives.