Acute myeloid leukemia (AML) is a hematologic malignancy with a poor prognosis. Recent genome-wide sequencing studies have identified frequent mutations in genes encoding members of the cohesin complex. Mutations in cohesin contribute to myeloid malignancies by conferring enhanced self-renewal of hematopoietic stem and progenitor cells but the mechanisms behind this phenotype have not been fully elucidated. Of note, cohesin mutations are highly prevalent in Down syndrome-associated acute megakaryocytic leukemia (DS-AMKL), where they occur in over half of patients. Evidence suggests that cohesin mutations alter gene expression through changes in chromatin accessibility and/or aberrant targeting of epigenetic complexes. In this review we discuss the pathogenic mechanisms by which cohesin mutations contribute to myeloid malignancies.