A 3 cm diameter mass from the metacarpus of a Puerto Rican Amazon parrot wa
s diagnosed as a granular cell tumour based on light microscopy. The cytopl
asmic granules were periodic-acid Schiff positive and diastase resistant. U
ltrastructural characteristics of the cells included convoluted nuclei and
the presence of numerous cytoplasmic tertiary lysosomes. This is only the s
econd granular cell tumour reported in a bird. We speculate that most granu
lar cell tumours are derived from cells that are engaged in some type of ce
llular degradative process, creating a similar morphologic appearance, but
lacking a uniform histogenesis.