Ovarian cancer is the second most common gynecologic malignancy and is one of the leading causes of death among women. The disease course and the accurate diagnosis are correlated with the early detection of the lesion. About 5% of ovarian cancers are poorly differentiated and difficult to be classified, and are referred to as undifferentiated carcinomas. They are usually large, solid with haemorrhage and necrosis, bilateral, and very difficult to be histologically classified. Generally, cases with undifferentiated components are very rare. The authors present a case of a young female patient with a rapidly progressive undifferentiated ovarian carcinoma and a final unfortunate clinical result.