Once the BED and MTD is determined in the Dose Escalation Segment, the Dose Expansion Segment will randomize patients with MDS, treatment naïve elderly AML, and relapsed/refractory AML patients to receive the BED or MTD dose. Relapsed/refractory AML patients may also receive SGI-110 on a daily x 10 schedule based on the total dose per cycle evaluated in the Dose Escalation Segment using the 5-daily regimen.