The case is a 68‒year‒old male, who had been diagnosed with acute myeloid leukemia(AML)prior to rectal cancer surgery, was referred to our hospital for treatment in July 2019. We planned to treat the AML first, and then the colorectal cancer. After completion of 1 course of CAG therapy(cytarabine, aclarubicin, G‒CSF), his white blood cell count increased sufficiently, so he underwent a robot‒assisted Hartmann operation in October. A second course of CAG therapy was started 15 days postoperatively. However, he was then diagnosed with exacerbation of the AML; remission induction therapy (daunorubicin, cytarabine)was started in November. In December, he developed a fever and abdominal pain, and on CT scan, it was discovered that an abscess had formed around the rectal resection site. Myelosuppression from AML led to prolonged sepsis; and by January 2020, the sepsis was systemic. His actual cause of death was given as circulatory failure. We report this, because only a few cases on the treatment of overlapping AML and colorectal cancers can be found in the literature.