Primary hypomagnesemia with secondary hypocalcemia (PHSH) is a rare type of hypocalcemic disorder which occurs in early infancy and is clinically characterized by recurrent tetany and/or convulsion. In this paper, a male infant with PHSH who had frequent seizures at the age of 9 days is described. Besides PHSH, several illnesses in infancy are manifested by hypomagnesemia and hypocalcemia, i.e. transient neonatal hypomagnesemic hypocalcemia, congenital renal or hepatic insufficiencies, magnesium-losing nephropathy, combined impairments of intestinal absorption and renal reabsorption of magnesium. PHSH is to be differentiated from these illnesses by the demonstration of a combination of the following findings; hypocalcemia refractory to calcium but responsive to magnesium, continuous requirement for magnesium supplementation to maintain normocalcemia, lack of hypermagnesiuria and/or impaired intestinal absorption of magnesium. Twenty cases from the literature were found to exhibit these characteristics. The clinical, biochemical, and endocrine features of PHSH are summarized on the basis of a review of the data of these and the present case. No associated illness was known in the afflicted infants or mothers. Both male and female infants were afflicted at a male to female ratio of 15:6. Some siblings were afflicted but none of the parents or relatives. The onset of tetany and/or convulsion was between the 9th day and 4th month, which is later than that of other neonatal hypocalcemic illnesses. Hypocalcemia was more pronounced than other infantile hypocalcemic illnesses. The role of the parathyroid hormone in the pathogenesis of hypocalcemia has been studied in several studies but no unifying concepts have yet been established.