1. The clinical and pathologic features of ovarian rupture (nongravid) are presented. Corpus luteum perforation is shown to be a more frequent cause of intraperitoneal hemorrhage than is follicular rupture. 2. The characteristic relationship between the time of ovarian rupture and the menstrual cycle is described. Follicular perforations occur at mid-interval and those of the corpus luteum during the latter half of the menstrual cycle. 3. The differential diagnosis between ovarian rupture, acute appendicitis, and ectopic pregnancy is discussed. 4. The treatment of ovarian rupture is usually laparotomy with conservation of the bleeding ovary. Nonsurgical treatment may be permitted if the diagnosis is certain. 5. Ten eases of corpus luteum rupture with intraperitoneal hemorrhage are reported. 1. The clinical and pathologic features of ovarian rupture (nongravid) are presented. Corpus luteum perforation is shown to be a more frequent cause of intraperitoneal hemorrhage than is follicular rupture. 2. The characteristic relationship between the time of ovarian rupture and the menstrual cycle is described. Follicular perforations occur at mid-interval and those of the corpus luteum during the latter half of the menstrual cycle. 3. The differential diagnosis between ovarian rupture, acute appendicitis, and ectopic pregnancy is discussed. 4. The treatment of ovarian rupture is usually laparotomy with conservation of the bleeding ovary. Nonsurgical treatment may be permitted if the diagnosis is certain. 5. Ten eases of corpus luteum rupture with intraperitoneal hemorrhage are reported.