Lenalidomide (CC-5013) is a structural derivative of thalidomide, with antiangiogenic and immunomodulatory effects. Fourteen patients with metastatic renal cell carcinoma (RCC) were enrolled on a phase 2 trial of lenalidomide administered orally at 25 mg daily for 21 days followed by a rest period of 7 days. The best response was stable disease in eight patients (57%) of the 14 evaluable patients. Toxicities included fatigue, hyperglycemia, dyspnea, and myelosuppression with decreased hemoglobin, lymphopenia, and neutropenia. Lenalidomide is tolerable, but no objective responses were observed in this clinical trial.