Controversy has arisen regarding the indications for elective surgical intervention in asymptomatic primary hyperparathyroidism (HPT). The present study was designed to answer two questions: Is untreated primary HPT a progressive disease over time? If not, are the risks attendant on long-term conservative management comparable to those obtained from surgery? Forty-seven patients with primary HPT, established by a persistently elevated serum calcium level and an inappropriately elevated parathormone value, who were managed conservatively and followed for a minimum of 5 years were identified. Serial data collection included calcium, phosphorus, albumin, creatinine, alkaline phosphatase, parathormone levels, skeletal x-ray films, and complications known to result from primary HPT. For each patient the collected data were divided into three equal periods of time (minimum of 20 months per period). In addition, the patients were classified into three groups based on their average serum calcium levels during the first observation period. No patient in any of the three groups experienced a significant progressive increase in serum calcium levels during the periods of observation. Sixteen of the 47 untreated patients (34%) experienced a complication usually associated with primary HPT: peptic ulcer disease (eight patients), decrease in renal function (five patients), renal calculus (one patient), hypercalcemic crisis (one patient), and ventricular conduction defect (one patient). Four deaths were attributed to these complications. In conclusion, the course of primary HPT and attendant complicating features are not accompanied by worsening of the hypercalcemia initially observed. None of the parameters studied offered an accurate prediction of likelihood, progression, or severity of complications. The risks associated with long-term nonoperative management of asymptomatic primary HPT are nevertheless considerable and exceed the morbidity and mortality rates resulting from neck exploration.