A 54-year-old man, who had been diagnosed with Loeys-Dietz syndrome based on his past history, family history, clinical findings, and the presence of a gene mutation, was referred to our hospital because of easy fatigability. Anemia, thrombocytopenia, and blasts in his peripheral blood were noted, and 31.4% blasts were found in a bone marrow aspiration. The blasts were positive for myeloperoxidase and esterase staining. Furthermore, karyotype analysis of bone marrow cells showed t(11;19)(q23;p13.1) and MLL abnormality was detected on RT-PCR A diagnosis of acute myeloid leukemia (M4) with 11q23 (MLL) abnormality was made. Loeys-Dietz syndrome is a Marfan-like congenital connective tissue disorder caused by a heterozygous missense mutation of a TGF-beta receptor I or II gene. The TGF-beta family inhibits the proliferation of normal epithelial cells and induces apoptosis, and is therefore known as a tumor suppressor factor. In this article, we discussed the association between Loeys-Dietz syndrome with a TGF-beta receptor gene mutation and cancer.