A 3-yr-old bearded dragon (Acanthodraco vitticeps) presented with lethargy, a swollen right elbow joint, inability to move its rear limbs normally, and marked leukocytosis. The majority of leukocytes were an abnormal mononuclear lymphoid-type cell with a high nuclear to cytoplasmic ratio, a slightly blue cytoplasm, nuclei with coarsely granular chromatin, and some nuclear clefts. Acute leukemia of lymphoid or myeloid origin was tentatively diagnosed. The abnormal mononuclear leukocyte cell population stained positively for the myeloid cytochemical stains: peroxidase, chloroacetate esterase, and L1-calprotectin. The abnormal cell population of the peripheral blood did not stain with the lymphoid cytochemical stains: α-naphthyl butyrate esterase, CD3, and CD79a.