Adnexal tumors can exist at any age. Most often they originate from the ovaries. We present a case of a 20-year-old female patient with a health history, who presented lower abdominal pain. She went to the Gynecology office where an increased volume of the left adnexal vaginal examination was found on ultrasound, a sep- tate cystic image corresponding to the left ovary was seen, it was interpreted as a follicular cyst and it was indicated to evolve. At 6 months of evolution it worsened and it was decided to perform a diagnostic-operative laparoscopy where a partial oophorectomy of the left ovary was performed. The pathological study determined the presence of a mature cystic ovarian teratoma. The patient evolved satisfactorily after the intervention.