RATIONALE: Myeloid sarcomas (MSs) are rare malignant hematological tumors. They most commonly occur in patients with acute or chronic myeloid leukemia. A de novo MS with no evidence of blood system disease is rare, but may represent the first sign of a systemic illness that precedes a full-blown disease. Herein, we report the computed tomography (CT) findings of an extremely rare case of a nonleukemic MS that progressed to acute myelogenous leukemia (AML) and simultaneously involved the small intestine, kidneys, mesentery, and mesenteric lymph nodes. Moreover, we provide CT findings before and after AML chemotherapy, which have not been reported previously. PATIENT CONCERNS: A 25-year-old man with intermittent upper abdominal pain for 6 months was admitted to the hospital on November 28, 2015. Initial CT showed concentric wall thickening of the jejunum with an adjacent mesenteric soft tissue mass and mesenteric lymph nodes enlargement. Both kidneys were involved as indicated by the presence of well-defined mildly dilated lesions. During the laparoscopic surgery, the small intestinal tumor, mesenteric soft tissue mass, and mesenteric lymph nodes were removed. DIAGNOSES: The pathological diagnosis was an MS. INTERVENTIONS: The patient refused systemic chemotherapy and was rehospitalized with persistently aggravated abdominal distension on February 17, 2016. Follow-up CT showed diffuse small bowel wall thickening, widespread infiltration of the peritoneum, omentum, and mesentery, mesenteric lymph node enlargement, and large amounts of ascites fluid. The lesions in both kidneys were substantially larger and more numerous than on initial CT. Then the patient was treated with conventional AML chemotherapy. OUTCOMES: The patient achieved complete hematological remission on bone marrow examination. Follow-up CT in September 4, 2016, showed none of the abnormalities seen on initial CT. Currently, the patient is in complete remission. LESSONS: If the radiological examination shows lesions at multiple sites, and these lesions are soft tissue masses with homogenous enhancement, MS should be considered in the differential diagnosis, and an aspiration biopsy should be performed to provide a definitive pathological diagnosis. If MS is diagnosed, systemic chemotherapy is crucial to recovery; otherwise, the disease may progress rapidly. Medical imaging is helpful for diagnosing MS and for monitoring treatment response.