Background: Hypomagnesemia is a frequent condition in patients with diabetes mellitus (DM). It could influence metabolic control in patients with DM. Relevant studies concern mainly adults and there are few data from the pediatric population. The aim of the present study was to evaluate magnesium levels and examine their possible association with glycemic control in pediatric patients with diabetes mellitus Methods: In all, 37 patients with DM (type 1, 32; type 2, 5) aged between 2 and 25 were included in the study. Using a cross-sectional design, we measured anthropometric parameters, HbA1c, serum magnesium, serum calcium, urinary magnesium, urinary calcium, lipid profile and parathyroid hormone. Hypomagnesemia was defined as magnesium levels 1.9mg/dL. Results: The mean age of the subject was 16.3 years. The mean duration of diabetes was 8 years. Hypomanesemia was found in 21 (56.8%) patients. Patients with hypomagnesemia showed significant higher HbA1c than patients without hypomagenemia (10.9 ± 2.9 vs 8.6 ± 2.9, P = 0.01). Serum magnesium levels were negatively correlated with HbA1c (r = -0.432; P = 0.008) as well as the duration of diabetes (r = -0.350; P = 0.034). Urinary calcium-creatinine ratio and urinary magnesium-creatinine ration were not different between the two groups. In lipid profiles, triglyceride was significantly increased in the group of hypomagnesemia (168.1 ± 96.7 vs 97.4 ± 47, P = 0.016). Prevalence of polyneuropathy was not different between the groups. Conclusions: Patients with DM are at risk of hypomagnesemia. Low serum magnesium levels in pediatric patients with DM could be involved in the development of poor glycemic control and chronic complications. We will compare the clinical and laboratory parameter after giving oral magnesium to hypomanesemia group.