There is evidence that lenalidomide has single agent activity in chronic lymphocytic leukemia (CLL)/small lymphocytic leukemia (SLL). Optimal dosing of lenalidomide in CLL has not been established yet. A pilot clinical trial in CLL studied single agent lenalidomide cycled every 4 weeks with 25 mg for three weeks on and one week off drug. In this trial dose reductions have been necessary secondary to prolonged neutropenia or thrombocytopenia in a majority of patients. However, there was also remarkable efficacy and evidence for an immune stimulatory effect of lenalidomide. Therefore, we propose this phase II trial using 20 mg lenalidomide (Revlimid(Registered Trademark)) 3 weeks on and 3 weeks off for 4 cycles in subjects who have been previously treated for chronic lymphocytic leukemia (CLL)/small lymphocytic leukemia (SLL). Subjects with at least partial response (PR) may go on to receive 4 additional cycles.