The prevalence of hypomagnesemia was studied in neonates and children. The specimens were selected randomly from those submitted to the clinical chemical laboratory for blood test. A serum magnesium concentration less than 0.74 mmol/L was considered hypomagnesemic. A total serum magnesium determinations of 910 patients showed that 188 (21.7% prevalence rate) patients contained low serum magnesium levels. Frequently encountered hypomagnesemia was found among neonates with clinical conditions as diarrhea 41 (21.8%), premature births 24 (12.8%), neonatal hepatitis 20 (10.6%) and respiratory distress syndrome 5 (2.7%). In children the clinical conditions most frequently encountered with low serum magnesium were seizure 30 (16%), renal disease 26 (13.8%), metabolic acidosis 18 (9.6%), ideopathic apnea 14 (7.4%) and tachycardia 10 (5.3%). The statistical analysis of low serum magnesium values of patients in various clinical groups showed a significant difference (p < 0.0001) upon using homogeneity of variances but this was insignificant with the application of Kruskal-Wallis 1-Way ANOVA since Chi-square = 12.5748.