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The hepatitis B virus (HBV) genotype was determined in a total of 121 plasma samples collected in France and the US from patients chronically infected with HBV. HBV genotype A was predominant in this collection, appearing in 66 samples (54%), while genotypes B, C, D, E and F occurred in 4 (3%), 14 (12%), 23 (19%), 1 (1%) and 0 (0%) of samples, respectively. However, the genotype of a total of 13 (11%) samples (2 from France, 11 from the US) could not be determined with the methodology used. Sequence analysis, and subsequent phylogenetic analysis of the complete genome and the individual open reading frames, showed that the virus isolate from these samples was 3248 bp long and, phylogenetically, did not cluster with any of the known genotypes. This strain was provisionally called HBV genotype G. Virus isolates that were obtained from geographically separated regions like France and the US were closely related to each other. All virus strains analysed contained some characteristic differences when compared to genotype A: a translational stop codon at aa 2 and 28 of the preCore region; a 36 nt (12 aa) insert in the amino-terminal part of the Core antigen (HBcAg); a 2 aa deletion in the carboxy-terminal part of HBcAg; and a 1 aa deletion in the preS1 open reading frame. The deduced amino acid sequence of HBsAg suggests that this newly discovered genotype G strain belongs to serological group adw2.