There are distinct ethnogeographic variations for the distribution of various hepatitis B virus (HBV) genotypes, and pathogenic and therapeutic differences are also observed. In general, genotype B infection has a relatively better prognosis than genotype C. In Thailand, genotypes C and B were reported as the major genotypes; however, there were no previous reports of HBV genotyping in the north of the country. From 1998 to 2000, 216 HBsAg-positive serum samples (164 males and 52 females, aged 16-52 years), were screened and collected from voluntary blood donors in four provinces of northern Thailand. The method of Naito et al. was employed in this study, with the multiplex-PCR approach and genotype-specific primers to identify genotypes A-F. We found that the HBV genotype C was highly predominant in northern Thailand (89.3%), when compared with the previous reports of genotype C distribution among voluntary blood donors from other areas in the country (50-65%), followed by genotype B (7.4%), mixed infection of genotype B and C (1.9%) and genotype A (0.5%). Four samples (1.9%) were unclassifiable. There was no significant difference of genotype distribution among four northern Thai provinces or each age group. © 2006 Elsevier Ireland Ltd. All rights reserved.