An otherwise healthy 16-year-old girl was brought to the emergency department due to persistent fatigue and microcytic anaemia. Upon physical examination in the emergency department, a palpable abdominal mass of firm consistency was found. For this reason, an ultrasound and a CT scan were performed, revealing a large mass of ovarian origin. Therefore, the patient was admitted for further investigations: blood exams showed elevated ovarian tumour markers and a gynecological evaluation was performed. The patient underwent annessectomy with omentectomy procedure via laparotomy. The histological result was compatible with FIGO stage IIIA dysgerminoma. Dysgerminoma is a rare ovarian tumour in paediatric age. Diagnosis is clinical, radiological, and laboratory-based and should be suspected in the presence of a rapidly growing abdominal mass associated with menstrual irregularities. It is an ovarian tumour with a favourable prognosis in most of the cases; indeed, it is aggressive only in 1/3 of cases. Treatment is primarily based on surgery, mostly conservative in early stages, while adjuvant chemotherapy to surgery is indicated in advanced stages.