This cross-sectional study investigated the prevalence and risk factors of hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV) infections among 266 drug users attending a drug-addiction treatment centre in Dhaka, Bangladesh, from November 1996 to April 1997. Of the 266 addicts, 129 were injectable drug users (IDUs), and 137 were non-injectable drug users (non-IDUs). The seroprevalences of hepatitis B virus surface antigen (HBsAg), anti-HBc, anti-HBs, and anti-HCV antibodies among the IDUs were 8 (6.2%), 41 (31.8%), 15 (11.6%), and 32 (24.8%), and among the non-IDUs were 6 (4.4%), 33 (24.1%), 9 (6.6%), and 8 (5.8%) respectively. None of the drug users were positive for anti-HIV antibody. Although the prevalence of HBV infection did not significantly differ between the IDUs and the non-IDUs, the prevalence of HCV infection was significantly higher among the IDUs. Among the IDUs, the prevalence of both HBV and HCV infections was associated with sharing of needles and longer duration of injectable drugs used. The seroprevalence of HBV infection in both IDUs and non-IDUs was significantly higher among those who had a history of extramarital and premarital sex. The prevalence of HCV infection was not associated with sexual promiscuity. There was no association between the seroprevalence of HBV and HCV infections and age. Active preventive programmes focusing on educational campaigns among the youths against substance abuse should be undertaken.