OBJECTIVES: To study the serum magnesium level in AKI and CKD, and its correlation with clinical manifestations and other biochemical parameters. DESIGN: A hospital-based cross sectional study. SETTING: Tertiary care teaching hospital in central India. SUBJECTS: Study population comprised of 75 cases of renal failure (50 CKD and 25 AKI) and 25 healthy control cases. METHODS: Studs populations included were subjected to a thorough history taking with special emphasis to exclude the presence of other diseases which are known to alter the magnesium levels in serum. Diagnosis of renal-failure was established by measuring raised clinical blood urea nitrogen and serum creatinine with clinical sign and symptoms of renal failure. Serum magnesium level is measured in "mg/dl" using metallochromic dye (Xylidyl) colorimetric assay. Relevant predefined clinical and biochemical parameters recorded from each subjects in all three groups. Data were computed and analyzed using SPSS statistical software. RESULTS: Hundred subjects were enrolled in the study, 75 cases of renal failure (50 CKD and 25 AKI) and 25 healthy control cases. Range of serum magnesium in controls was 1.32 to 2.4mg/dl with a mean 1.856(±0.2959). Mean blood urea, serum creatinine, sodium, potassium, calcium and magnesium level were 127.65 mg/dl, 6.75mg/dl, 135.24 MEq/L, 4.86 MEWL, 9.28mg/dl and 2.89mg/dl respectively in AKI cases, and 111.36mg/dl, 7.02 m2/d1, 135.01 MEq/L, 4.93 MEq/L, 8.99mg/dl and 2.75mg/dl respectively in CKD cases. Eight (16%) CKD cases had central nervous system depression with their mean serum magnesium level of 3.61 mg/dl. Four (16%) AKI cases had central nervous system depression with mean serum magnesium level of 3.47mg/dl. CONCLUSION: Serum magnesium level has prognostic significance in severity in AKI and CKD and CNS symptoms. Baseline serum magnesium should be done in every case of CKD and AKI with other electrolytes and renal function tests. There is positive correlation between serum magnesium and blood urea, creatinine & potassium while negative correlation between serum magnesium and serum sodium & calcium levels both in AKI and CKD case.