Elevated serum concentrations of 1-84 parathyroid hormone (PTH) after operation for sporadic parathyroid adenoma have been reported in previous studies, years after operation for primary hyperparathyroidism (pHPT). The cause and significance of this finding have not been elucidated. Primary hyperparathyroidism was diagnosed in 195 patients from January 1987 to December 1998. Operation for pHPT was performed in 124 patients. To evaluate long-term effects of elevated serum 1-84 PTH, biochemical variables and pre- and postoperative diseases were investigated from hospital case records. Of the 124 patients operated on, 103 had a solitary adenoma. Among these patients, 60 had normal serum concentrations of 1-84 PTH and calcium postoperatively, 38 patients had follow-up for more than 12 months (range 12-207 months-group A). Persistent elevated serum concentrations of 1-84 PTH and normocalcemia were found in 23 patients. Fourteen patients had follow-up for more than 12 months (range 15-76 months-group B). Two patients had persistent pHPT, and 18 were normocalcemic, but in this retrospective study data on serum 1-84 PTH were not available. No significant differences were found between groups A and B at the time of diagnosis concerning clinical characteristics. More that 12 months after operation for pHPT, the patients in group B, with persistent elevated serum concentrations of 1-84 PTH, had a significantly (c2 = 11, p = 0.005, and power of test 0.66) higher frequency of cardiovascular diseases from ischemic heart disease and hypertension. Persistent elevated serum concentrations of 1-84 PTH after operation for sporadic parathyroid adenoma may be associated with development of cardiovascular disease. This group of patients therefore needs lifelong control and, possibly, medical intervention.