Since the first case of a unilateral tubal twin pregnancy was reported by Deott in 1891, on average, one case is reported per year in the literature. Ninety-nine such cases have been described and the present case is described as the one hundredth. The unilateral twin pregnancies were diagnosed during or after surgery in all but two cases. Santos et al. described the first unilateral, tubal twin pregnancy to be diagnosed before surgery through the use of ultrasound. Sherer et al. describe the second such case detected by ultrasound from the beating of the fetal heart by the abdominal ultrasound probe. We describe here the first case of unilateral, tubal twin pregnancy to be documented by ultrasound, with cardiac activity of two foetuses detected by the endovaginal probe. Furthermore, this case was treated by laparotomy, which had not previously been described.