Inclusion Criteria:

          1. Subjects must be at least 18 years of age;

          2. Subjects must be post-allogeneic transplant from any donor source;

          3. Subjects must have either:

               1. High risk CD34+ AML (de novo or secondary, and any WHO 2008 classification
                  excluding acute promyelocytic leukemia). High risk AML is defined as (a) disease
                  status beyond complete remission (CR) #1 at transplant or (b) treatment related
                  AML or (c) presence of adverse cytogenetics including inv(3); t(3;3); t(6;9);
                  t(v;11); -5 or del(5q); -7; abnl(17p) or complex karyotype; or

               2. High risk CD34+ MDS (WHO 2008 classification). High risk is defined as (a) blast
                  count ≥5% at the time of transplant or (b) treatment related MD or (c) presence
                  of adverse cytogenetics including -7/del7q or complex karyotype;

          4. For AML subjects, they must have a documented CR within 45 days prior to allo-HCT;

          5. For MDS subjects, they must have < 20% myeloblasts in the bone marrow within 45 days
             prior to allo-HCT;

          6. Subject Karnofsky performance status must be ≥ 70;

          7. Subjects must be platelet transfusion independent (Platelet transfusion independence
             is defined as 7 days or greater without a platelet transfusion);

          8. Neutrophil count ≥ 1.0 thou/mm3 and platelet count ≥ 30 thou/mm3;

          9. Subjects must have total bilirubin ≤ 2 mg/dL;

         10. Subjects must have serum AST and ALT levels ≤ 2.5 times upper limit of normal;

         11. Subjects must have serum creatinine < 2.5 times upper limit of normal and a calculated
             creatinine clearance > 30 ml/min by Cockcroft-Gault formula (see Appendix I:
             Cockcroft-Gault Creatinine Clearance Calculation);

         12. All study participants who will receive lenalidomide based on the CD34+ chimerism
             testing must be registered into the mandatory Revlimid REMS® program, and be willing
             and able to comply with the requirements of the REMS® program;

         13. Females of child-bearing potential (i.e., women who are premenopausal or not
             surgically sterile) may participate, provided they meet the following conditions:

             a) Females of reproductive potential must adhere to the scheduled pregnancy testing as
             required in the Revlimid REMS® program; and

         14. Written, voluntary informed consent, willingness, and ability to comply with all study
             procedures.

        Exclusion Criteria:

          1. CD34- AML or MDS;

          2. Inability to give informed consent;

          3. Uncontrolled active infection(s) requiring intravenous antibiotics;

          4. Known or suspected hypersensitivity to lenalidomide;

          5. Grade II-IV acute GVHD or extensive GVHD;

          6. Not able to swallow the lenalidomide capsule as a whole;

          7. Female subjects who are pregnant or nursing.