A 12-year-old female black-masked lovebird (Agapornis personata) with a cobalt color mutation was presented for self-mutilation of a mass located on the right lateral neck. Cytologic evaluation of the soft tissue mass revealed a predominance of poorly stained mast cells with metachromatic intracytoplasmic granules. The presumptive diagnosis was cutaneous mast cell tumor. Clinical evaluation, results of a complete blood cell count and biochemical analysis, and radiographs did not reveal systemic manifestation of mast cell disease. The mass was surgically resected, but surgical margins were limited because of the location of the mass and the small size of the patient. The lovebird died the day after surgery. Gross postmortem examination revealed splenomegaly, multifocal pinpoint white nodules throughout the liver parenchyma, severe thickening and yellow coloration of the great vessels, and pale pink swelling of the caudal right kidney. Histopathologic analysis of the resected mass revealed sheets of round cells that contain metachromatic granules, defined as neoplastic mast cells, within a fine fibrovascular stroma. Similar neoplastic cells were seen in the right kidney, hepatic sinusoids, splenic pulp, periovarian connective tissue, and bone marrow. The histopathologic diagnosis was a cutaneous mast cell tumor and disseminated mast cell disease, or mastocytosis. To the authors' knowledge, this is the first reported case of a cutaneous mast cell tumor and mastocytosis in a psittacine bird.