This is a Phase I, open-label, multi-center, dose-escalation study of lenalidomide in adult patients with newly diagnosed, relapsed or refractory acute myeloid leukemia. All patients will receive lenalidomide per oral daily (starting dose is 25 mg/d). Cohorts of 3 patients (to be expanded up to 6 if 1 dose-limiting toxicity (DLT) is observed among the first 3 patients) will be sequentially allotted to progressively higher dose levels of lenalidomide on the basis of the presence and severity of lenalidomide-related toxicity or lenalidomide related serious adverse reactions encountered in the first cycle. For the purpose of this study, patients' enrollment will continue until the maximum tolerated dose (MTD) will be determined and characterized.