The findings of 152 patients with proven primary hyperparathyroidism are reportedmthe purpose of the analysis was to find difference between the various clinical manifestations of the disease. Furthermore the occurrence of acute hyperparathyroid crisis in our series as well as in the literature are described. 65.8% of the patients were females, 34.2% were males. The leading symptom in 98 patients (group I) were kidney stones and in 23 patients (group II) cystic bone disease. Both manifestations of the disease occurred in only 7 patients (group III) and no symptoms related to the kidneys or to the bones occurred in 24 patients (group IV). Because of the difference of the clinical manifestations the additional data were analyzed for each group separately and compared with each other. There was no difference in the mean serum calcium levels for all four groups, however, patients of group I were on the average younger, the duration of the disease was longer and the weight of the parathyroid adenoma was lower compared to the other three groups, Data are presented regarding calcium excretion, phosphate clearance and tubular reabsorption of phosphate for each group. At operation single or multiple adenoma formation was present in 133 patients, whereas diffuse hyperplasia was found in 17 and carcinoma in 2 other patients. 46 of the adenomas were found in an atypical anatomical localisation. This observation is responsible for the many unsuccessful or second explorations of the neck; The weight of the adenomas varied between 0.1 and 23.5 g. The most difficult diagnosis was that of diffuse hyperplasia. The sucess of the surgical intervention was usually established in over 80% of the cases within 24 to 48 hours after the operation with a significant fall of serum calcium. There ist still no definite explanation for the variability of the clinical manifestations of primary hyperparathyroidism. Parathyroid hormone determinations on larger numbers of patients are not yet published. The assumption, that different hormones or peptide fragments are reposible for the different action on bone and kidney is discussed; In our series of 152 patients acute hyperparathyroid crisis occurred eight times. Our findings are compared to the other well documented cases in the literature. Main symptoms were nausea, vomiting, abdominal pain and different states of cerebral dysfunction. Most of the patients had calcium levels over 16 mg/100 ml. Partial renal insufficiency with elevated blood urea and phosphate retention was found in over 50% of the cases. Overall mortality of all cases with acute parathyroid crisis is 52.5%. The pathogenesis of acute hyperparathyroidism and the implications of high calcium levels are discussed. According to our own experience hypercalcenia can be controlled with an intensive therapeutic program and emergency operation for acute parathyroid crisis is no longer necessary.