Introduction: Diabetes mellitus is the most common endocrine disorder, encountered in practice. The incidence of diabetes is increasing at a rapid pace and is evolving into an epidemic. Methodology: In the present study, serum magnesium levels of 100 diabetic patients are compared with 30 nondiabetic patients with age and sex-matched controls. Serum magnesium levels are significantly low amongst diabetics as against nondiabetic controls giving the incidence of hypomagnesemia in diabetics to be 66%. Results: Amongst diabetics serum magnesium levels are adversely influenced by factors like male gender, longer duration of diabetes, poor glycemic control, higher serum cholesterol levels, hypertension as well as micro and macrovascular complications showing significant prevalence. Values of serum magnesium are significantly low in patients with microvascular complications as against those with macrovascular complications. Diabetic ketoacidosis is significantly associated with lower serum magnesium levels. However, age group, type of diabetes, presence of infection do not influence serum magnesium levels in the present study group. Conclusion: consider magnesium deficiency as a prognostic factor influencing the progression of diabetic complications and justify the therapeutic role of magnesium supplementation in achieving the reduction in insulin resistance, better glycemic control and slowing down of progressive diabetic complications.