<b><i>Introduction:</i></b> The coexistence of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) with different gynecologic neoplasms is a rare phenomenon. Here, we report a case of simultaneously developed CLL/SLL with endometrioid-type uterine cancer. <b><i>Case Report:</i></b> A 58-year-old woman was admitted to the 2nd Department of Gynecology, Lublin Medical University, Lublin, Poland, in June 2017, where the uterine cancer was diagnosed. After the surgery, pathological examination revealed a uterine moderately differentiated adenocarcinoma of endometrioid subtype (subtype I according to Bokhman) deeply infiltrating the myometrium as well as the uterine cervix. Surprisingly, CLL/SLL was subsequently diagnosed in all removed pelvic as well as para-aortic lymph nodes. Immunohistochemical analysis showed CD45 (++), CD20 (+), CD3 (–/+), CD19 (+), CD23 (+), CD5 (+), and CD34 (+). Proliferative activity, assessed by MIB-1 proliferative index immunostaining, reached 18%. The patient was admitted to radiotherapy and chemotherapy at the Oncology Hospital, Lublin, Poland, and is still on follow-up. <b><i>Conclusions:</i></b> The coexistence of CLL/SLL with various gynecological malignancies, especially primary human endometrial cancer, is a rare entity. The detection of both tumors simultaneously, in general, is accidental, and the management should not be different from the situation in which malignancy appears de novo.