Introduction: Cross-sectional studies have reported an increased frequency of vitamin B12 deficiency in type 2 DM specially in metformin users. Type 1 DM may be associated with pernicious anemia and celiac disease, resulting in vitamin B 12 deficiency. Subjects and methods:100 patients with type 2 DM, 30 patients with type 1 DM, and 20 healthy volunteers as control. Demographic and anthropometric data, metformin therapy and dosage were recruited from patients attended internal medicine clinic, Benha University Hospital. Laboratory data were collected in the form of CBC, FBG, hemoglobinA1c, lipid profile, Kidney function tests, Liver function test, and Vitamin B12 levels. Results: There was nonsignificant difference among the three groups regarding age, sex, residence, and duration of DM. Serum B 12 level was statistically lower in type 2 & type 1 DM compared to control group (p < 0.001). In type 2 DM, we identified 66 % with low vitamin B 12 level (10% were deficient, and 56 % were insufficient level of the vitamin). While, in type 1 DM, 6.7 % of patients had vitamin B 12 deficiency and 60 % had insufficient level. Metformin users in type 2 DM had a significant lower vitamin B 12 level (p= 0.048). In type 1 DM, low vitamin B 12 level was insignificantly associated with Metformin use. Conclusion: We found 66 % and 66.6 % with low vitamin B 12 in type 2 and type 1 DM respectively. Metformin therapy is associated with vitamin B12 deficiency in type 2 DM.