Genotypic analysis of 203 evaluable sample pairs with HBV DNA ≥ 1,000 copies/ ml at week 104 demonstrated that the primary mutation associated with telbivudine resistance was rtM204I, often associated with mutations rtL180M and rtL80I/ V and infrequently with rtV27A, rtL82M, rtV173L, rtT184I and rtA200V.