Development of hepatitis B virus (HBV)-resistant strains following nucleos(t)ide analog treatment is a major medical concern. This report describes a case of an adult patient with chronic HBV infection, sequentially treated with the nucleos (t)ide analogues, lamivudine, adefovir, and entecavir. During monotherapy with lamivudine, the patient developed lamivudine-resistant variants, which were undetectable during adefovir dipivoxil monotherapy. Twenty-two months after discontinuing lamivudine therapy, the resistant variants were again detected while the patient was receiving entecavir monotherapy. Genotypic analysis by sequencing the HBV polymerase was confirmed with the INNO-LiPA method. The results of this study suggest that entecavir treatment reselected residual lamivudine-resistant HBV variants, possibly because lamivudine-resistant HBV is less susceptible to entecavir than the wild-type virus. Despite the presence of these variants, the patient has had a complete virological response. J. Med. Virol. 79:1671–1673, 2007. © 2007 Wiley-Liss, Inc.