The clinical presentation of primary hyperparathyroidism has changed considerably after the application of biochemical autoanalysers. The condition was previously found with characteristic symptoms in bone, kidneys and the gastrointestinal tract; less than 1% of patients were assumed to be asymptomatic. Today, most patients have mild and uncharacteristic symptoms. Primary hyperparathyroidism has been detected with increasing frequency in the western world, but there are large variations within demographically otherwise comparable areas. There are also regional differences regarding the incidence of surgical treatment of the disease. Demographic studies have shown increased morbidity and mortality primarily from cardiovascular and possibly malign diseases related to hypercalcemia. Follow-up studies based on surgical series have shown increased mortality related to preoperative serum calcium level. In view of the altered clinical picture of primary hyperparathyroidism, treatment of moderate and possibly "benign" primary hyperparathyroidism has been actualised. At an international consensus conference in 1990, this patient group was defined by an arbitrary serum calcium limit of 3.0 mmol/l, but this limit has been found to be unacceptably high. Regardless of where the upper limit is set, there are so far well accepted indications for surgery, but only one in two patients fulfil these criteria. A working group of endocrinologists and endocrine surgeons from nine university clinics in Scandinavia have recently initiated a prospective, randomised study evaluating surgical treatment and a systematic follow-up of patients with borderline primary hyperparathyroidism.