SummaryWe describe the interrelationship of the urinary excretion of sodium, calcium, magnesium, and phosphorus in 22 hypocalcemic premature neonates whose mean gestational age was 31.7 wk. Strong relationships between sodium excretion and calcium excretion (r= 0.85), sodium excretion and magnesium excretion (r= 0.76), sodium excretion and phosphorus excretion (r= 0.61), and calcium excretion and magnesium excretion (r= 0.94) were demonstrated. Sodium intake during the 84‐hr study period ranged from 2.9 to 34.5 mEq/kg and calcium intake during the same period ranged from 0 to 152.3 mg of elemental calcium per kg. The intakes of the other cations were negligible. All variables but phosphorus excretion (r= −0.55) were independent of calcium intake whereas sodium excretion (r= 0.76), calcium excretion (r= 0.72) magnesium excretion (r= 0.62), and phosphorus excretion (r= 0.53) were all correlated with sodium intake. Serum calcium concentration at the end of the study was unrelated to total calcium intake during the 84‐hr study period, whereas it was negatively related to total sodium intake (r= −0.71).SpeculationWe suggest that sodium intake and sodium exeretion exert significant control over the excretion of calcium, magnesium, and phosphorus in sick, hypocalcemic, premature neonates. High sodium intake in this group of patients is associated with a lowered serum calcium concentration; thus, increased sodium intake and perhaps increased calcium excretion may play a role in the development or exacerbation of early onset neonatal hypocalcemia.