In this case report a patient with thyroid dysfunction who received chronic treatment with interferon-alpha (INF-alpha) following a diagnosis of chronic myelogenous leukemia (CML) is described. Generally INF-alpha induced dysthyroidism develops in the earlier phase of INF-alpha treatment. This is a case report of thyroid dysfunction which occurred 4 years after the patient began to receive INF-alpha administration. In addition, INF-alpha was administered to this patient for a longer period than those reported in the literature.