Chondrocalcinosis is known to be common in hyperparathyroidism. In order to discover the effect of parathyroidectomy on chondrocalcinosis and to investigate this association further, we studied two groups of patients. In one group were 41 postparathyroidectomy patients, and in the other 100 admissions to the acute geriatric unit. The total incidence of chondrocalcinosis in the parathyroidectomy group was 32%, and in the elderly control group 11%. There was little or no osteoarthrosis in these patients. It was found that chondrocalcinosis occurred in the normal population from the age of 75 and in the hyperparathyroid group from the age of 45. In both groups the incidence rose steadily with age. In the hyperparathyroid group alone, preoperative serum calcium levels were no different in those without chondrocalcinosis, suggesting that hypercalcaemia alone is not a sufficient stimulus for chondrocalcinosis. Those with chondrocalcinosis had higher mean preoperative alkaline phosphatase levels, nearly twice as much radiological bone disease, and were older. Parathyroidectomy had no effect on attacks of pseudogout or on preexisting cartilage calcification. A connection with high levels of circulating parathyroid hormone is suggested, and a link with physical age-related changes in cartilage postulated.