A total of 224 diabetics and 221 non-diabetics (control) were involved in this study, to determine the relative incidence of diabetes mellitus in ABO/Rhesus blood group. The current criteria for the diagnosis f diabetes mellitus were applied in differentiating the diabetics from the non-diabetics. Blood group, fasting blood sugar (FBS) and random blood sugar (RBG) were determined using standard methods. Type I, Type II and gestational diabetes mellitus were identified in this study. Biodata information were obtained during history taking and from subject hospital case note. The mean age of diabetics was 50.9 + 11.4 (SD) with age range of 24-72 years. Mean age for control was 49.21 + 9.25 with age range of 24-70 years. There were no significant differences between the mean ages of the two groups. Blood group O- and A+ were significantly (P<0.01) higher among the diabetics than non diabetics. Blood group O+ was significantly (P<0.01) lower in diabetics than in the control population. Blood group O- and A+ therefore appears to be more susceptible to diabetes mellitus.