Between January 1991 and September 1991 424 patients were operated on for hyperparathyroidism (HPT) at the Department of Surgery, University of Heidelberg. In 8.5% of cases a persistent HPT was present. Our own rate of persistence was 5.4%. Ultrasound revealed the pathology in 44.2% while highly selective venous catheterization identified the correct side in 63.4%. 70% of all patients with persistent HPT required one operative revision, the remaining 30% having up to 3 revisions. 27 patients (75%) were operated on successfully. In 12 of these patients an ectopic adenoma was found. The adenoma was not identified intraoperatively in 2 patients (6.9%). One patient sustained permanent damage to the recurrent laryngeal nerve.