To analyze the occurrence of transformation from myelodysplastic syndrome (MDS) to acute myeloid leukemia (hereinafter referred to as transformation from MDS to AML) in patients with myelodysplastic syndrome with a deletion 5q cytogenetic abnormality (hereinafter referred to as del(5q)MDS) who received Revlimid® 5 mg Capsules (hereinafter referred to as Revlimid) and who are continuing or no longer continuing Revlimid treatment.