The prevalence of hepatitis A, B, C, and D viruses was studied in 467 military personnel with human immunodeficiency virus type 1 (HIV-1) infection. Antibody to hepatitis C virus (antiHCV) by first-generation ELISA was found in 136 (29%). Of sera repeatedly reactive for antiHCV by first-generation ELISA, two-antigen recombinant immunoblot assay (RIBA) was positive in 41 (32%) and four-antigen RIBA was positive in 55 (41%). Four-antigen RIBA was positive in 33 (30%) ofthe 109 with an OD on ELISA of ⩽2.0 compared with 22 (81%) of the 27 with an OD >2.0 (P <.001). Anti-HCV detected by four-antigen RIBA was associated with increasing age, black or Hispanic race, and antibody to hepatitis B core antigen. When patients with hepatitis B surface antigen were excluded, elevated alanine aminotransferase was found in 5 (8%) of 63 with a negative RIBA and 13 (28%) of 47 with a positive RIBA (P = .006). While RIBA was negative in more than half of those with anti-HCV by ELISA, 55 (12%) of these HIV-1 infected personnel had anti-HCV detected by RIBA, which was associated with a strong reaction by ELISA, elevated liver enzymes, coinfection with hepatitis B, minority race, and older age.