A reversible syndrome of headache, altered mental status, seizures and cerebral visual abnormalities with neuroradiological studies suggesting predominantly posterior white matter abnormalities has been described. This syndrome has been referred to as posterior reversible encephalopathic syndrome (PRES). PRES has been associated with hypertensive encephalopathy, eclampsia and treatment with immunosuppressive or cytotoxic agents. Rare case reports describe association with hypercalcemia. We present a patient with AIDS, Mycobacterium avium intracellulare related hypercalcemia with posterior reversible encephalopathic syndrome.