Because of a high prevalence of hepatitis C virus (HCV) infection (10-20%) among veterans seeking care in Department of Veterans Affairs (VA) hospitals, current US military forces were evaluated for HCV infection. Banked serum samples were randomly selected from military personnel serving in 1997 and were tested for antibody to HCV (anti-HCV). Overall prevalence of anti-HCV among 10,000 active-duty personnel was 0.48% (5/1,000 troops); prevalence increased with age from 0.1% among military recruits and active-duty personnel aged <30 years to 3.0% among troops aged >/=40 years. Prevalence among 2,000 Reservists and active-duty troops was similar. Based on sequential serum samples from 7,368 active-duty personnel (34,020 person-years of observation), annual incidence of infection was 2/10,000. Of 81 HCV RNA-positive troops for whom genotype was determined, genotypes 1a (63%) and 1b (22%) predominated, as in the civilian population. These data indicate that HCV infection risk among current military forces is lower than in VA studies and the general civilian population aged <40 years. The low level of HCV infection may be attributed to infrequent injection drug use in the military due to mandatory testing for illicit drugs prior to induction and throughout military service.