Patients undergoing malabsoprtive operations for bariatric surgery are prone to disturbances of bone metabolism, but this does not commonly lead to clinical symptoms. We present a morbidly obese patient who had undergone the biliopancreatic diversion of Larrad, and presented clinical symptoms of severe hypocalcemia and tetany after total thyroidectomy. Very high doses of i.v. calcium and calcitriol and 10 days of hospitalization were required to control the symptoms and correct plasma levels. The physiological aspects that contribute to this situation are discussed.