Metastatic uterine tumors originating from extragenital cancers are a rare clinical occurrence. We report a case of metastatic uterine cancer derived from small-cell lung cancer (SCLC) that necessitated surgical treatment. The patient was a 59 y/o female who had undergone chemotherapy for stage IIIB SCLC. A 15 cm uterine tumor lesion was initially detected on CT scans. The patient had previously been diagnosed with uterine fibroids, but compared to the most recent CT scans taken one and a half months earlier, imaging diagnosis revealed a sudden increase in the size of the tumor when compared to the 8 cm myoma fibroid noted previously. Additional work-up with MRI scans revealed T2-enhanced images of a tumor that had almost completely invaded the myometrium; the tumor presented with marked diffusion-weighted enhancement, and a flow void was noted within the tumor. A differential diagnosis of uterine sarcoma was considered, but due to the lack of focal hemorrhage or necrosis findings on MRI imaging, the possibility of differential diagnosis of metastatic SCLC was also noted. As the patient was experiencing abdominal symptoms including abdominal distension and tenderness due the tumor, a simple hysterectomy and bilateral salpingo-oophorectomy were performed to palliate the symptoms. During the surgical procedures, intra-abdominal findings noted peritoneal dissemination while intraoperative cell cytology diagnosis of ascites revealed small-cell cancer. The final histopathological diagnosis likewise revealed metastatic small-cell cancer from the primary lung cancer. The clinical status of the lung cancer was evaluated as progressive disease (PD), and a change in chemotherapy regimen was necessitated. Further disease progression was noted on CT scans at 2 and a half months after surgery, and with gradual systemic disease progression, the patient died of disease at 3 months postsurgery. Initial evaluation of rapidly enlarging uterine tumors should include a differential diagnosis of uterine sarcoma; additionally, it is necessary to also consider the rare possibility of metastatic disease as in the present case with a clinical history of extragenital malignancy.