We aimed to study the prevalence and clinical implications of hepatitis B virus (HBV) subgenotypes in Chinese patients. A total of 4,300 patients, mainly from northern China, were enrolled, including 182 patients with acute hepatitis B and 4,118 patients with chronic HBV infection who had been exposed to nucleoside or nucleotide analogs. HBV genotypes/subgenotypes were determined by direct sequencing of the HBV S/Pol region. The prevalence rates were 0.40% for HBV/B1, 14.30% for HBV/B2, 0.25% for HBV/B3, 0.35% for HBV/B4, 1.05% for HBV/C1, 81.72% for HBV/C2, 0.93% for HBV/C3, 0.16% for HBV/C4, and 0.84% for HBV/D. In chronic HBV infection, patients with HBV/B2 were younger and had lower ⌯BeAg positive rates than patients with HBV/C2. The incidence of lamivudine-resistant mutations was significantly higher in HBV/C2 compared to HBV/B2 (27.9% versus 19.8%; P < 0.01), and the significant difference was observed only for rtM204I and not rtM204V. In addition, compensatory mutations were more frequently detected in HBV/C2. The incidence of adefovir-resistant mutations was similar between the two subsets, but HBV/C2 inclined to show rtA181V (3.6% for C2 versus 0.9% for B2; P < 0.01), while HBV/B2 inclined to show rtN236T (4.5% for versus 2.5% for C2; P < 0.01). The ratios of HBV/B2 to HBV/C2 infection were 1.7 (110/65), 5.7 (2,653/463), 7.5 (520/69), 8.0 (48/6), and 15.3 (183/12) for acute hepatitis B, chronic hepatitis B, liver cirrhosis, acute-onchronic liver failure, and hepatocellular carcinoma, respectively. In conclusion, HBV/C2 and HBV/B2, two prevalent subgenotypes, differ in lamivudine-and adefovir-resistance-associated mutational patterns. HBV/ C2-infected patients are more likely to have disease progression than HBV/B2-infected ones.Hepatitis B virus (HBV) infection remains a serious health problem that currently affects about 350 million people worldwide and 93 million in China (12,20). HBV infection is associated with a wide spectrum of clinical presentations, including asymptomatic subclinical infection, acute hepatitis B (AHB), chronic hepatitis (CHB), liver cirrhosis (LC), acute-on-chronic liver failure (ACLF), and hepatocellular carcinoma (HCC). Factors associated with disease progression remain largely unknown. Viral factors have been implicated in the pathogenesis and clinic outcome of HBV infection (23).HBV exhibits a mutation rate of around 2 ϫ 10 4 base substitutions/site/year, which is an approximately 100 times higher than that of other DNA viruses (5). HBV is at least classified into eight genotypes, based on nucleotide sequence divergence among strains of Ͼ8%. In Asia, HBV genotypes B and C are the predominant genotypes, and HBV genotype C is associated with more severe liver disease, delayed HBeAg seroconversion, and a high risk of HCC (7,8,10,17,18,24). Within each HBV genotype, subgenotypes have been identified based on a 4 to 8% difference in the complete nucleotide sequence. HBV/B, HBV/C, and HBV/D have been individually classified into five subgenotypes each, namely, HBV/B1 through HBV/ ...