We report the results of short-term tamoxifen treatment (20 mg two times a day orally) in 2 patients with metastatic medullary thyroid carcinoma. Patient A had a rapid tumor progression with development of Cushing's syndrome before initiation of tamoxifen treatment. Patient B had a slowly progressive course. In both cases, neither clinical nor biochemical improvement were observed, after 1 and 3 months of tamoxifen therapy, respectively.