Acute suppurative thyroiditis (AST) is quite rare, even in immunocompromised patients. The authors describe 2 cases of AST during aggressive chemotherapy for acute myelogeneous leukemia (AML). They were treated with aggressive combination chemotherapy and achieved complete remission. After several courses of chemotherapy, they developed fever and pain in the region of the thyroid gland. Laboratory tests showed hyperthyroidism and elevated levels of thyroglobulin and C-reactive protein. Ultrasonography revealed hypoechoic areas in the thyroid gland. A diagnosis of AST was made. Bacterial infections were suspected because they were sucessfully treated with antibiotics. After a month, the patients' thyroid function and thyroglobulin levels returned to normal without a period of transient hypothyroidism. A pyriform sinus fistula was not demonstrated. The results suggest that neutropenia and preceding cellulitis around the thyroid gland, which might be subsequent to oral mucosal damage induced by anticancer drugs, may play a role in the development of AST. AST should be considered a potential complication of aggressive chemotheragy for leukemia.