Behçet's disease (BD) is a multisystem inflammatory vasculitis of unknown etiology and pathogenesis. Coexistence of BD along with hematological malignancies is extremely rare. We describe a patient diagnosed with BD and chronic myelomonocytic leukaemia (CMML) with trisomy 8. This case suggests that trisomy 8 may be involved in the concurrent manifestation of myelodysplastic syndrome (MDS) and BD with gastrointestinal ulcers.