Patients who undergo a Roux-en-Y gastric bypass (RYGB) procedure are at moderate risk for calcium and vitamin D deficiency. Those who subsequently undergo thyroid or parathyroid surgery are at high risk for developing severe symptomatic hypocalcemia if they are not monitored and adequately treated prophylactically. We describe the case of a morbidly obese 40-year-old man who had undergone RYGB surgery 6 months prior to the discovery of metastatic papillary thyroid carcinoma. He subsequently underwent total thyroidectomy with central and bilateral neck dissection. Following surgery, he developed severe symptomatic hypocalcemia, as his calcium level fell to a nadir of 6.0 mg/dl. He required aggressive oral and intravenous repletion therapy with calcium, vitamin D, and magnesium for 10 days before hospital discharge. Providers should institute careful preoperative screening, patient counseling, and prophylactic calcium and vitamin D therapy for all thyroid surgery patients who have previously undergone RYGB surgery to prevent the development of severe and life-threatening hypocalcemia. Only a few reports of patients have been published on the dangers of thyroid and parathyroid surgery in patients who have undergone bariatric surgery. We report a new case to add to the body of literature on this patient population. We also review calcium homeostasis and supplementation as they relate to this situation.