Human Immunodeficiency Virus (HIV) and Hepatitis B Virus (HBV) constitute serious public health problems worldwide. In Sierra Leone, information on both viral infections remains scanty. This study estimated the seroprevalence of HIV and HBV infections and a possible co-infection in one hundred and ninety-eight (198) patients seeking diagnosis at a private laboratory in Freetown, Sierra Leone. Blood plasma was collected from each patient after informed consent was obtained. The samples were assayed for antibodies to HIV virus and HBV antigen using appropriate assays. Male patient accounts for 52% of the population examined. Thirty-one (31) of the 198 patients examined (15.7%) were positive for HIV. Hepatitis B surface antigen (HbsAg) was present in 17 (39.5%) females and 26 (60.5%) males. Thirteen (13) (6.6%) patients were co-infected with HIV and HBsAg. This is the first documented evidence of HBsAg and HIV co-infection in Sierra Leoneans. Larger population based studies are however needed to confirm the findings.