Seventeen cases of spontaneous, partial or total vaginal rupture, in pregnant ewes, involving the dislocation and hemiation of the intestines and uterus, were studied. Four of them also had a uterine torsion, and three of these recovered after treatment In the remaining 13 cases the condition of the uterus was unknown. The lesion always consisted of a dorsolateral tear in the vagina with a partial or total perforation of the wall close to the uterine cervix. The affected animals were all in normal body condition. Their average age was just under five years, and most were carrying twins. Most cases occurred approximately one week before expected lambing. None of the cases was observed to have a vaginal prolapse before the vaginal rupture. Histological examination of one case revealed scar formation in the vaginal wall close to the rupture, which appeared to be due to an earlier inflammatory process or injury. The circulatory disturbance in the reproductive organs caused by the uterine torsion potentially weakens the vaginal wall. This weakness, in combination with excessive tenesmus resulting from increased tension in the uterine ligaments, and in some cases possibly with a lower vaginal resistance due to previous scarring, may be of aetiological significance in spontaneous vaginal rupture.