Ovarian pregnancy is an uncommon presentation of ectopic gestation, where the gestational sac is implanted within the ovary. Usually, it ends with rupture, which occurs before the end of the first trimester. Its presentation often is difficult to distinguish from that of tubal ectopic pregnancy and hemorrhagic ovarian cyst. We describe a case of primary ovarian pregnancy in a 31-year-old patient who presented to the emergency room with symptoms and signs of peritonism and positive urine hCG test. The gestation sac was demonstrated in the right ovary by transvaginal sonography. MSD (mean sac diameter) was 15 mm corresponding to the sixth gestational week. Free fluid was found in the Douglas pouch. Culdocentesis was positive for hemoperitoneum. Henceforth, emergency laparotomy and wedge resection of the ovary was perfomed. Aetiological, clinical and therapeutical aspects of this rare extrauterine pregnancy are described. Also, the problems of its differential diagnosis are discussed.