OBJECTIVE: The peri-operative and immediate post-operative outcome of secondary hyperparathyroidism treated with subtotal parathyroidectomy is reported. METHODS: We studied 100 patients with chronic renal failure who underwent subtotal parathyroidectomy at our department. Surgical eligibility was based on hyperparathyroidism stage, defined by symptoms of osteodystrophy and/or the presence of hypercalcemia and hyperphosphatemia refractory to medical treatment. Parathormone levels were measured pre-operatively and during the first post-operative days. RESULTS: During surgery, four parathyroid glands were identified in 86% of patients, five glands in 1%, and less than four glands in 13%. The ratio of hyperplastic to normal glands was 93:7. No correlation was found between anatomic location of the glands and the presence of hyperplasia. Parathormone decreased to normal or very low values in 93% of the patients. In seven cases, the lowest post-operative parathormone value was above 30 pg/ml, although four glands were removed in four of these patients. In 95% of the patients with four or more identified glands, post-operative serum parathormone levels decreased to normal or very low values. In 23% of the patients with less than four glands, parathormone levels remained too high. On the other hand, post-operative parathormone values normalized in 10 patients who had less than four glands identified during surgery; in two of them, parathyroid tissue was found during postoperative pathological examinations of the resected thyroid lobe. CONCLUSIONS: Subtotal parathyroidectomy is an acceptable treatment in patients with refractory hyperparathyroidism. Our results indicate that there was not a perfect correlation between the number of identified glands and post-operative parathormone in a subset of patients.