Hepatitis B virus (HBV) genotypes differ in their potential for causing disease. Consecutive patients with chronic HBV infection (CHBV) (n=122) and blood donors (n=67) positive for hepatitis B surface antigen and HBV DNA were genotyped using polymerase chain reaction-restriction fragment-length polymorphism. The ratio of male to female subjects was significantly higher in the blood donor group than in the group of patients with CHBV (P=.0004). Among patients with CHBV, genotype D was detected in 57.3%, genotype A was detected in 18%, and genotype C was detected in 11.5%. Only genotypes D and A were detected in blood donors. The difference between the detection rate of genotype C in patients with CHBV and in blood donors was significant (11.5% vs. 0%; P=.009). Patients with CHBV who had genotype C had higher alanine transaminase (ALT) levels than those who had genotype A (P=.044) or genotype D (P=.014). Detection of genotype C in patients with CHBV and the association of genotype C with higher ALT levels may predict that this genotype has a greater potential for causing disease than other genotypes.