Thalidomide has become a novel agent in the treatment of multiple myeloma and many other hematological and solid malignancies. Thalidomide has various adverse effects including neurologic, hematologic, cardiovascular, gastrointestinal, and endocrinologic toxicities. However, with strict regulations for use, there have been few case reports of thalidomide toxicity. A 42-year-old man presented with both breast engorgement and tenderness for 1 year. Six years ago, he had been diagnosed malignant histiocytosis at left palpable axillary mass lesion. He was treated with chemotherapy according to Langerhans cell histiocytosis. But, 6 months later, the response of chemotherapy was refractory and then, he has been received thalidomide salvage therapy (25-100 ㎎/day) for 5 years. Mammography and ultrasonography revealed a bilateral heterogeneous mixed echoic lesion suggesting a fibroglandular tissue under the nipple and subcutaneous layer. We have treated him with bromocriptine. With a follow-up of 15 months, gynecomastia and breast discomforts were improved.