We describe two male infants suffering from primary hypomagnesaemia, diagnosed at 3 months and 2.5 months of age. They both presented with generalised convulsions, with case 2 exhibiting hypocalcaemia which did not respond to calcium and case 1 having normocalcaemia at first but hypocalcaemia 3 days after admission. Both improved dramatically after initiation of magnesium therapy. A carrier-mediated transport defect is the most likely cause of this disease. It is of the utmost importance that a correct and prompt diagnosis be made as therapy is simple and effective. Failure in diagnosing this condition could prove fatal as demonstrated in the family history of case 2.