Background: Nontuberculous mycobacterium is a recognized cause of hypercalcemia, particularly in patients with acquired immunodeficiency syndrome (AIDS). Here we describe a case of severe hypercalcemia secondary to Mycobacterium abscessus (M. abscessus) in a patient with AIDS. To the best of our knowledge this is the first case report describing a case of M. abscessus presenting as retroperitoneal lymphadenopathy and severe hypercalcemia. Case description: A 56-year-old man with AIDS presented with altered mental status and somnolence for four days. Laboratory investigations were significant for calcium 16.49 mg/dL (RI 8.9-10.3 mg/dL), 1,25 dihydroxyvitamin D level 44.1 pg/ml (RI 19.9-79.3 pg/ml) and parathyroid hormone (PTH) 4 pg/mL (RI 15-65 pg/mL). CT scan of Abdomen and Pelvis showed hepatosplenomegaly with large retroperitoneal, retrocrural, and mesenteric lymphadenopathy which had an intense focal uptake on Gallium scan. Bone marrow biopsy revealed mild plasmacytosis (5%) with no evidence of myelodysplasia, acute leukemia or lymphoma. A subsequent lymph node biopsy showed fragments of fibrous tissue with lymphohistiocytic infiltrate and many acid-fast bacilli. Pre-antibiotic blood cultures grew Mycobacterium which was identified later as M. abscessus at four weeks. Conclusion: hypercalcemia in HIV-infected patients may suggest malignancy or infectious etiology, among other causes. Clinicians should be aware of the risk of hypercalcemia with nontuberculous mycobacterium (NTM) infection, whether as first manifestation or a late presenter in the disease course after initiating antiretroviral therapy (ART). We suggest careful monitoring of serum calcium level upon diagnosis of NTM infection and after initiation of ART, NTM therapy or vitamin D supplementation.