The patient is a 44-year old man with recurrent renal stones who was f
ound to have ''normocalcemic hyperparathyroidism'' due to a large para
thyroid adenoma that was successfully removed. This case has important
implications for other normocalcemic renal stone formers who would be
labeled ''idiopathic.'' The dilemma of the patient with a definite di
sorder whose screening tests are ''within the normal range'' is discus
sed briefly.