"Anti-HBc alone" which is an unusual serologic pattern of hepatitis B virus (HBV) infections, may be detected in the seropositive samples for hepatitis C virus (HCV), human immunodeficiency virus (HIV) infections and in the presence of autoantibodies due to cross reactions. In this study, 20 serum samples with isolated antibody to hepatitis B core antigen, which were detected in May 2005, have been investigated by means of the presence of some autoantibodies (anti-nuclear antibody; ANA and rheumatoid factor; RF), anti-HCV and anti-HIV, in the Central Laboratory of Dicle University Medical School. All of the "anti-HBc alone" samples were negative for HBV-DNA by real-time polymerase chain reaction (PCR), and liver enzyme (ALT and AST) levels were normal except for three patients. As a result, a total of six (30%) samples were found positive. Four of them were positive for ANA and two were positive for anti-HCV, while one serum yielded positivity for both ANA and anti-HCV. Anti-HCV positive samples were searched for the presence of HCV-RNA by real-time PCR, and none were found positive. Of three patients with increased AST and ALT levels, one was anti-HCV positive, one was ANA positive, while the other was negative for all parameters. In conclusion, possible presence of autoantibodies and anti-HCV should be taken into consideration during the evaluation of isolated anti-HBc IgG positive test results.