Background The aim of this study was to present a case of simultaneous occurrence of ovarian endometriosis and cystic teratoma of the ipsilateral ovary in a patient who underwent laparoscopic adnexectomy.Methods We presented the case of a 35 y patient admitted to Clinic “Narodni Front” in Belgrade for laparoscopic surgery of a left ovarian cyst.The patient’s medical history indicated a healthy female.The patient reported intermittent pelvic pain and dysmenorrhea in the past three months. A 2D transvaginal ultrasound was performed, and the findings included a normal uterus and right ovary.A biloculated cyst 50x50mm was visible on the left ovary.The capsule of the cyst 3mm with septum 2.6mm.One of the cysts 30x25mm with heterogeneous pattern, which consisted mostly of anechoic with one hyperechoic part.The second cyst was anechoic 20x25mm was characterized by a homogenous pattern.Ascites of minimal volume was noted in the pouch of Douglas.Colour flow Doppler of pericystic vessels RI 0.55.Serum chemistry and complete blood count were normal. Increased levels of CA-125-48 IU/l. Results Laparoscopy revealed normal findings in the following internal organs: the uterus, right adnexa, left Fallopian tube, omentum, parietal peritoneum, liver, small and large intestines.A smooth-capsulated cyst, partially filled with dark brown fluid was visible on the left ovary.Left adnexectomy was performed using LCS. Definitive diagnosis was ovarian endometriosis and a mature cystic ovarian teratoma in the same ovary.Malignant components were not identified.Conclusions Simultaneous occurrence of endometriosis and a mature teratoma in the ipsilateral ovary is very rare and literature describes only a few such cases.