Hypomagnesemia is common in diabetic subjects, and is especially common in poorly controlled diabetes, suggesting that diabetes low serum magnesium status is osmotic diuresis-dependent. To assess the relationship between serum magnesium and HDL-cholesterol concentration adjusted by serum glucose values. We assessed the serum magnesium levels of 50 controlled (HbA(1c)</=7.5% and FPG<126 mg/dl), 110 non-controlled (HbA(1c)>7.5% and FPG>/=126 mg/dl) type II diabetic patients, 40 subjects with impaired fasting glucose (IFG) (FPG>/=110 mg/dl and <126 mg/dl) and 190 healthy volunteers (FPG<110 mg/dl). Healthy volunteers were required to have normal blood pressure and normal laboratory tests. Subjects in the groups included were matched by age and body mass index (BMI). The average of diabetes duration was of 11.4+/-6.6, and 10.9+/-6.2 years, P=NS, for the controlled and non-controlled diabetic patients, respectively. Thirty (60.0%) controlled diabetic subjects, 58 (52. 7%) non-controlled diabetic patients, 21 (52.5%) subjects with IFG, and 39 (20.5%) healthy volunteers had serum magnesium levels </=1.7 mg/l. Serum HDL-cholesterol value showed significant graded increase with serum magnesium levels irrespective of glucose values. Results of this study suggest that hypomagnesemia by an etiopathogenic pathway glycemia independent seems to be involved to decrease HDL-cholesterol.