Primary hyperparathyroidism (PHP) might be characterized by either prevailing bone or renal stone patterns with different metabolic features. To explore the possibility of different hormonal patterns we studied 129 patients with PHP: 95 stone formers (SF) and 34 nonstone formers (NSF). Females prevailed over males in both groups. Severe and specific bone lesions were more evident in NSF than SF. Parathyroid gland histology displayed a prevalence of adenoma in NSF, whereas isolated hyperplasia prevailed in SF. SF had lower levels of serum Ca, urinary Ca, ALP and serum PTH than NSF. As expected serum 1,25-dihydroxyvitamin D [1,25(OH)2 D] levels were greater in both groups of patients than in controls but we found no difference between the two groups. 25-Hydroxyvitamin D was neither increased with respect to controls nor different between groups. We conclude that patients with PHP may represent well separated metabolic and clinical entities, but we cannot confirm that serum 1,25(OH)2D levels play a key role in discriminating the different clinical features. In addition, the findings of predominant parathyroid hyperplasia in SF and the clinical evidence of recurrent hyperparathyroidism only in these patients suggest the possibility that the endocrine disorder might be the consequence over time rather than the cause of nephrolithiasis.