Therapy-related acute myeloid leukemia (AML) is a rare but potentially fatal adverse event caused by chemotherapy or radiotherapy. Herein we report a patient diagnosed with therapy-related AML 2 months after chemoradiotherapy for esophageal cancer. A 61-year-old man with dysphagia was diagnosed with locally advanced esophageal cancer with para-aortic lymph node metastasis. Laboratory blood test did not reveal any abnormality except mild macrocytic anemia. To alleviate dysphagia due to malignant esophageal stenosis, the patient underwent concurrent chemoradiotherapy of 60 Gy in 30 fractions with cisplatin and 5-fluorouracil at a local area in thoracic esophagus. Dysphagia alleviated during chemoradiotherapy; however, pancytopenia did not recover after the completion of chemoradiotherapy, and general fatigue with fever developed 13 weeks after the last day of chemoradiotherapy. To rule out hematological malignancy, bone marrow biopsy was performed. The bone marrow smear and flow cytometry analysis indicated the development of AML. Chromosomal test revealed a complex karyotype, suggesting that AML was associated with myelodysplastic syndrome. The patient died 1 month after the diagnosis of therapy-related AML. Thus, the findings indicate that therapy-related AML may develop during the acute phase of chemoradiotherapy and bone marrow biopsy is necessary when prolonged pancytopenia exists after chemoradiotherapy.