To examine the association between serum magnesium levels and C-reactive protein (CRP) in non-diabetic, non-hypertensive obese subjects.Cross-sectional study.A total of 371 subjects, 101 men and 270 women. Of them 138 lean (37.2%), 133 (35.9%) overweight, and 100 (26.9%) were obese, matched by age.Fasting and 2 h serum glucose following a 75 g oral glucose load. Fasting serum total cholesterol, HDL- and LDL-cholesterol, triglycerides, C-reactive protein (CRP), albumin; and magnesium levels; urinary protein excretion; body mass index (BMI), waist-to-hip ratio (WHR), and blood pressure.The presence of CRP was documented in four (2.9%) lean, 13 (9.8%) overweight, and 20 (20.0%) obese subjects, and decreased magnesium levels (equal or less than 1.8 mg/dl), in 2 (1.45%) lean, 7 (5.2%) overweight, and 19 (19%) obese subjects. The lowest serum magnesium levels and the highest CRP concentrations were documented in the obese subjects. Twenty-three (82.1%) of the subjects with low serum magnesium (five overweight and 18 obese) showed CRP concentration equal or more than 10 mg/l. There was a graded significant decrease between CRP concentration and serum magnesium levels (r = -0.39, P = 0.002). The odds ratio (CI95%) between magnesium and CRP adjusted by age, sex, BMI and glucose tolerance status for the subjects within the low quartile of magnesium distribution was 2.11 (1.23-3.84).The results of this study show that low serum magnesium levels are independently related to elevated CRP concentration, in non-diabetic, non-hypertensive obese subjects.