Inclusion Criteria:

1. Patients with untreated CLL or small lymphocytic lymphoma (SLL) with indication to treatment according to NCI Working Group guidelines.Patients that have received single agent rituximab will be allowed to participate in this study.
2. Age 65 or older
3. ECOG/WHO performance status of 0-2.
4. Adequate renal function indicated by serum creatinine less or equal to 2 and adequate hepatic function indicated as total bilirubin less or equal to upper level of normal and as ALT less or equal 2 ULN.
5. Able to understand and sign Informed Consent after the investigational nature, study design, risks and benefits have been explained.
6. Able to adhere to the study visit schedule and other protocol requirements.
7. Disease free of prior malignancies for 5 years with exception of currently treated basal cell, squamous cell carcinoma of the skin, or carcinoma "in situ" of the cervix or breast. Patients with malignancies with indolent behavior such as prostate cancer treated with radiation can be enrolled in the study as long as they have a reasonable expectation to have been cured with treatment modality received.
8. Females of childbearing potential (FCBP). A female of childbearing potential is a sexually mature woman who: 1) has not undergone a hysterectomy or bilateral oophorectomy; or 2) has not been naturally postmenopausal for at least 24 consecutive months (i.e., has had menses at any time in the preceding 24 consecutive months). Must have a negative serum or urine pregnancy test with a sensitivity of at least 50 mIU/mL within 10-14 days prior to and again within 24 hours of starting lenalidomide and must either commit to continued abstinence
9. Continued from above. from heterosexual intercourse or begin TWO acceptable methods of birth control, one highly effective method and one additional effective method AT THE SAME TIME, at least 4 weeks before she starts taking lenalidomide. FCBP must also agree to ongoing pregnancy testing.
10. Men must agree to use a condom during sexual contact with a female of child bearing potential even if they have had a successful vasectomy.
11. All patients must be counseled at a minimum of every 28 days about pregnancy precautions and risks of fetal exposure. See Appendix J: Risks of Fetal Exposure, Pregnancy Testing Guidelines and Acceptable Birth Control Methods, AND also Appendix M: Education and Counseling Guidance Document.
12. All patients must be able to take aspirin (81 or 325 mg) daily as prophylactic anticoagulation (patients intolerant to ASA may use warfarin or low molecular weight heparin.

Exclusion Criteria:

1. Known sensitivity to thalidomide or its derivatives.
2. Documented prolymphocytic leukemia (prolymphocytes more than 55% in the blood).
3. Known positivity for HIV or active hepatitis (B or C).
4. A serious medical condition, laboratory abnormality or psychiatric illness that would interfere with the ability of the patient to participate in this program according to the judgement of the Principal Investigator.
5. Active cardiovascular disease as defined by the New York Heart Association Class 3 or 4.
6. History of erythema nodosum if characterized by a desquamating rash while taking thalidomide or similar drugs.
7. Concurrent use of other chemotherapy agents.
8. Pregnant or breast feeding females. Lactating females must agree not to breast feed while taking lenalidomide.
9. No known history of tuberculosis or recent exposure to tuberculosis.