The unusual occurrence of epilepsy and hypocalcemia in the same family is described. Epilepsy was present in three siblings (convulsive generalized in two females and partial in one male). All six family members had calcium ion, plasmatic phosphorus, plasmatic and erythrocytic potassium, urine calcium and phosphate concentration below the normal levels. Altered values of calcium-induced potassium membrane permeability were found in three subjects (two of them also affected by epilepsy). The assumption that alterations of membrane structure or function play an essential role in determining familial epilepsy and that the normal "set point" for calcium is genetically determined in familial hypocalcemia could explain the concomitance of both pathologies to some extent.