This is a phase 1/2, dose-escalation trial of Lenalidomide given in combination with idarubicin + cytarabine. During phase 1, we will enroll patients with AML involving del 5q31; 2) patients with MDS RAEB-2 associated with monosomy 5 or segmental deletion involving 5q31, either alone or with additional cytogenetic abnormalities, and 3) older patients with any type of karyotypic profile in whom an effective and reliable standard of care remains to be developed. All 3 groups of patients define a population of patients with very poor prognoses. Dose escalation of lenalidomide will use a standard 3x3 design. Dose escalation of Lenalidomide only will take place, while the doses of idarubicin and cytarabine will be constant. This trial will have an induction component, consolidation component, and maintenance component. Overall safety and MTD will be determined from the induction phase only.