The association of Behçet's disease with myelodysplastic syndromes has been established in the hematologic, gastrointestinal, and medical genetics literature; trisomy 8 is a feature present in 70% of these reports. Because trisomy 8 is ordinarily present in only 14% of patients with myelodysplastic syndrome, this is a significant overrepresentation. We describe a patient with recurrent aphthous stomatitis who was subsequently diagnosed with trisomy 8-positive myelodysplastic syndrome after an unexplained macrocytosis was further investigated.