Genitourinary system lymphomas comprise a small part of extra-nodal lymphomas (ENLs). ENLs of uterine origin are extremely rare and are often confused with gynecological malignancies. We present an 80-year-old female patient diagnosed with diffuse large B-cell lymphoma (DLBCL) with a single focus of the uterus. The patient's only complaint was abnormal uterine bleeding. Magnetic resonance imaging revealed an intramural-subserous-submucous multiple mass lesion with minimal contrast enhancement mimicking leiomyosarcoma. Diffuse pathological 18F-fluorodeoxyglucose uptake was detected in the entire uterus corpus and cervix on positron emission tomography/computed tomography (PET/CT) scanning. The pathology of the endocervical and endometrial curettage material obtained was DLBCL; the patient was diagnosed with ENL, and a single focus was the uterus. ENLs should be considered in the differential diagnosis of gynecological malignancies in patients with abnormal uterine bleeding. PET/CT is crucial in showing metabolically active spread areas in these patients.