Occult hepatitis B virus (HBV) infection, characterised by the presence of HBV infection with undetectable hepatitis B surface antigen (HBsAg), was investigated in 98 Lebanese patients with chronic hepatitis C liver disease and 85 control subjects recruited from eight institutions in different parts of the country. The prevalence of occult HBV infection ranged from 11.9% to 44.4% in hepatitis C virus (HCV)-infected patients and it increased with increasing severity of the liver disease. The overall rate of HBV DNA in our 98 HCV-infected patients was 16.3%. On the other hand, the rate of HBV DNA was 41.0% in anti-HBc alone positive patients compared to only 7.1% in healthy controls who were also anti-HBc alone positive (p < 0.001). Moreover, the prevalence HBV DNA increased with increasing severity of the liver disease, but this increase was only marginally significant and, perhaps, could have been significant if more patients were involved in the study. Although Lebanon is an area of low endemicity for both HBV and HCV, occult HBV infection is common in HCV-infected patients. The presence of HBV DNA, therefore, presents a challenge for the effective laboratory diagnosis of hepatitis B, particularly if polymerase chain reaction (PCR)-based HBV detection methods are not used.