A septate uterus, the most common structural uterine anomaly, is caused by the abnormal development of the Müllerian ducts during embryogenesis. It is infrequently detected, with an estimated prevalence of around 2 % in women of reproductive age [1]. The diagnosis of a septate uterus depends on an accurate classification of congenital uterine anomalies by the American Society for Reproductive Medicine (ASRM) system [2]. A septate uterus is associated with poor reproductive outcomes, such as a high incidence of recurrent miscarriages, premature delivery, stillbirth, subfertility, and infertility [3].

Endometriosis, defined as the presence of glands and stroma of the endometrium outside the uterus, is common in adolescents who have an obstructed reproductive tract [[4], [5], [6]]. In terms of pathogenesis, the disease can be attributed to multiple factors, including coelomic metaplasia, retrograde menstruation, and metastasis. Endometriosis affects 2–17 % of women of reproductive age and often presents as abnormal menstrual bleeding, dysmenorrhea, chronic pelvic pain, deep dyspareunia, subfertility, and primary amenorrhea; however, some patients are coincidentally identified in adolescence due to associated anomalies like a septate uterus [7].

A septate uterus results from the incomplete resorption of the medial septum after fusion of the Müllerian ducts, the association between a septate uterus and endometriosis has been previously described [[8], [9], [10]]. One theory is that a septate uterus causes peristaltic disturbance, which increases the possibility of developing menstrual blood reflux and endometriosis. While the other theory is Müllerian remnant, which argues that at the onset of puberty, under the influence of rising sex hormones, cellular debris from embryonic Müllerian ducts transforms into endometriotic tissue. In most cases, a septate uterus affects fertility. A relatively large septate uterus directly affects the implantation of fertilized eggs, whereas a relatively small septate uterus can cause miscarriage and stillbirth, even if the fertilized egg is implanted successfully. Endometriosis further affects the fertility of patients with a septate uterus. Most women suffering from a septate uterus and endometriosis are in childbearing age, for whom poor reproductive function is a serious concern. The combined presence of endometriosis and a septate uterus need precise diagnostic imaging to diagnosis and is an indication for early surgery to improve their reproductive function. More attention should be given to the intervention and prognosis of such patients.

This study aimed to describe the clinical characteristics and treatment outcomes of patients who have a septate uterus complicated by endometriosis, including complete septate uterus complicated by endometriosis and incomplete septate uterus complicated by endometriosis. Particular emphasis is placed on the patient's reproductive function, drawing the clinician's attention to these patients.