The genus Helicobacter comprises several species of both gastric and enterohepatic intestinal bacteria. H. pylori, the type species of the genus, is associated with gastritis, peptic ulcer and gastric cancer in humans. H. pylori genome has a high number of restriction and modification (R-M) systems and their diversity is useful for strain typing. To analyse if such a high number of expressed methyltransferases is a characteristic of the genus Helicobacter, the genomic methylation of five non-pylori Helicobacter spp. (H. canadensis, H. canis, H. felis, H. mustelae and H. pullorum) was determined. The results revealed that the number of R-M systems among nonpylori Helicobacter spp. is smaller than those observed among a group of 221 H. pylori strains (p<0,001), but is greater than those observed for the mean of all bacteria sequenced genomes (p=0,005). 16S ribosomal RNA analysis of H. pylori sequenced strains and five non-pylori Helicobacter spp. clearly isolate H. pylori species. Surprisingly, the analysis of the genomic methylation status by MCRM algorithm performs similarly. This suggests that R-M systems do not appear to be spread in a miscellaneous manner, once even that these genes may be subjected to acquisition and loss; their expression still allows discriminating among Helicobacter spp.