Inclusion Criteria:

- Histologically confirmed diagnosis of CLL or SLL as established by the NCI Working
Group Response Criteria (NCI 96 Criteria).

- Received one or more prior therapies for CLL.

- Patients must have symptomatic disease requiring therapy as defined by the protocol.

- >/= 4 weeks from prior cancer therapy.

- ECOG performance status of
- All study participants must be registered into the mandatory RevAssist® program, and
be willing and able to comply with the requirements of RevAssist®.

Exclusion Criteria:

- Prolymphocytic leukemia (PLL).

- Richter's (large cell) transformation.

- Prior allogeneic transplant within 12 months or prior allogeneic transplant > 12
months currently receiving immunosuppressants.

- Active autoimmune hemolytic anemia.

- CNS involvement.

- Chronic enteral corticosteroids > 10mg prednisone or equivalent.

- Evidence of laboratory TLS by Cairo-Bishop Definition of Tumor Lysis Syndrome

- Use of any other experimental drug or therapy within 28 days of baseline

- Major surgery within 28 days of baseline.

- Known hypersensitivity to thalidomide.

- The development of erythema nodosum if characterized by a desquamating rash while
taking thalidomide or similar drugs.

- Any prior use of lenalidomide.

- Known seropositive for or active viral infection with human immunodeficiency virus
(HIV), hepatitis B virus (HBV) or hepatitis C virus (HCV).