BACKGROUND: Hypercalcemia in adults has several less common causes. Management in patients with chronic kidney disease (CKD) is challenging because bisphosphonates are contraindicated. This case presents an uncommon cause of hypercalcemia in a subacute rehabilitation patient who was managed with denosumab. CASE REPORT: A 79-year-old female with CKD stage 4 was admitted to a skilled nursing facility with a limited-weight-bearing status after right-hip arthroplasty. Four weeks later, she developed hypercalcemia (11.5 mg/dL; normal, 7.9-9.9 mg/dL) with serum albumin of 2.5 g/dL (corrected calcium, 12.7 mg/dL). Despite iv fluids, hypercalcemia worsened (corrected serum calcium, 14.5 mg/dL), and she was rehospitalized. Additional studies eliminated common causes of hypercalcemia, leading to the diagnosis of immobilization hypercalcemia. Due to CKD, a bisphosphonate was not given. She received 10 doses of calcitonin s.c. with mild improvement in her calcium, and she returned to the skilled nursing facility. Because hypercalcemia worsened within days, denosumab 60 mg was administered s.c., and her serum calcium level normalized. Over the next several weeks, her surgical wound worsened. Hip x-ray showed osteolysis of her residual right femoral head. In retrospect, hip x-ray during her hospitalization for hypercalcemia showed osteolysis, likely from osteomyelitis. A contribution of osteomyelitis to hypercalcemia could not be excluded. Despite resolution of hypercalcemia, she succumbed to sepsis. CONCLUSION: Immobilization hypercalcemia is underappreciated in post-acute care older adults. In this patient with CKD, denosumab reversed her hypercalcemia; however, the case highlights potential risks and limitations with this therapy and emphasizes the need for further studies in medically complex older adults.