We have studied 1765 patients attending our clinic during 1991, with the aim of determining the prevalence of HDV and HIV infection in our country in two populations at risk for parenteral and sexual HBV transmission. A second objective was to determine whether or not HBV-HIV co-infection was associated with a greater risk for HDV. Our findings indicated that sexual transmission of VHD is not common, unlike parenteral transmission, and that there is a significantly greater prevalence of infection with HDV in Chi-square who have the HBsAg complex and are HIV positive.