This case report will give an example for the necessity of performing an ultrasound examination of the neck before resection of the parathyroid glands. In end-stage renal failure a 38-year-old man developed secondary hyperparathyroidism (HPT). Four glands were removed. Two years later the patient revealed persisting HPT. At this point an ultrasound examination was performed and demonstrated a fifth parathyroid gland located inside the thyroid gland. The case illustrates the benefit of cervical ultrasound, even in cases of secondary hyperparathyroidism, prior to any cervical exploration.