Inclusion Criteria:

   - Age ≥ 18 years at the time of signing the informed consent form

   - Must be able to adhere to the study visit schedule and other protocol requirements

   - Must have a documented diagnosis of B-cell CLL

   - Must be relapsed or refractory to at least 1 regimen for treatment of CLL. At least
   one of the prior treatments must have included a purine analog-based or
   bendamustine-based regimen

   - Must have an Eastern Cooperative Oncology Group (ECOG) performance status score of ≤
   2.

Exclusion Criteria:

   - Any serious medical condition, laboratory abnormality, or psychiatric illness that
   would prevent the subject from signing the informed consent form

   - Active infections requiring systemic antibiotics

   - Systemic treatment for B-cell CLL within 28 days of initiation of lenalidomide
   treatment

   - Alemtuzumab therapy within 120 days of initiating lenalidomide treatment

   - Prior therapy with lenalidomide

   - History of grade 4 rash due to prior thalidomide treatment

   - Planned autologous or allogeneic bone marrow transplantation

   - Central nervous system (CNS) involvement as documented by spinal fluid cytology or
   imaging.

   - Uncontrolled hyperthyroidism or hypothyroidism

   - Venous thromboembolism within 12 months

   - ≥ Grade 2 neuropathy

   - Uncontrolled autoimmune hemolytic anemia or thrombocytopenia

   - Disease transformation [i.e. Richter's Syndrome (lymphomas) or prolymphocytic
   leukemia]

   - Participation in any clinical study or having taken any investigational therapy within
   28 days prior to initiating lenalidomide therapy