A retrospective survey was performed on 265 patients with primary hyperparathyroidism who had received three forms of treatment on a non-randomised basis. 'Successful' surgery (normalisation of serum calcium) was carried out in 142 patients, 'unsuccessful' surgery (persistence of hypercalcaemia after neck exploration) in 33 and no surgery in 90. Patients subjected to surgery were significantly younger than patients in the unoperated group and their serum calcium values at the time of decision were approximately 10 per cent higher. The mean follow-up period was significantly longer in the operated groups. The percentages of patients who had died were similar in each group. Clinical events relating to renal stones depended on the presence or absence of calculi at the time of decision rather than on the method of treatment. At the time of follow-up the prevalence of hypertension, renal impairment and vertebral crush fractures were similar in all three groups. Forearm osteo-densitometry showed a higher bone mineral content in the 'successful' group than in the other two groups. In spite of the selection bias inherent in a study of this kind, it is clear that untreated hyperparathyroidism is compatible with long survival and a lack of demonstrable deleterious effects on kidney and bone.