Only 12 myelodysplastic syndrome (MDS) cases with Behçet's syndrome have been previously reported and trisomy 8 was found to have accumulated in all these patients. Five of the cases had complications in the form of multiple intestinal ulcers, which is one of the symptoms of Behçet's syndrome. To investigate the relationship between trisomy 8 and multiple intestinal ulcers in MDS patients, we analyzed 46 MDS cases treated in our hospital over the last decade, and trisomy 8 was observed in eight of them. Three of these cases had complications of both multiple intestinal ulcers and thrombosis, and two cases showed episodes of thrombosis without intestinal ulcers. All these five cases featured trisomy 8, while the other 38 MDS patients without trisomy 8 had no episode of either intestinal ulcer or thrombosis. Two of the three cases suffering from multiple intestinal ulcers were treated with granulocyte-colony stimulating factor (G-CSF), which resulted in aggravation of the symptoms. Although the influence of G-CSF on such symptoms in MDS patients with trisomy 8 remains unclear, it seems advisable to exercise caution in the use of G-CSF when an MDS patient with trisomy 8 has intestinal ulcers or thrombosis.