Background: To determine the relationship between ABO/rhesus (Rh) blood groups and type 2 diabetes mellitus in a western Algerian population. Method: This case-control study was conducted at the Regional Hospital Centre of Maghnia, Tlemcen, from July 2008 to May 2009, involving 280 patients with type 2 diabetes mellitus and 271 healthy controls. Blood samples were collected from the patients after consent had been obtained. The samples were tested for ABO and Rh blood groups, using the Beth-Vincent and Simonin-Michon methods. The allele frequencies were calculated according to the Bernstein formulas. Results: The χ 2 test results showed that there was no association between the ABO blood group and type 2 diabetes mellitus. It was also noted that the O blood group was distributed with the highest frequency among diabetic subjects (52.85%). For the Rh system, d allele frequency presence was higher in diabetics than in nondiabetics (0.3778 and 0.3644 respectively). The difference between phenotype frequencies was not significant (p = 0.733). The distribution of ABO/Rh blood groups between gender and ethnic group showed no significant difference (p > 0.05). Conclusion: Our study confirms that there is no association between ABO/Rh blood group and diabetes mellitus in this Algerian population.