In-vitro fertilization (IVF) and ovarian stimulation are frequently performed in patients with endometriosis. Although endometriosis is a hormone-dependent disease, the rate of IVF complications related to endometriosis is low. We report four cases of severe digestive complications due to the rapid growth of sigmoid endometriosis under ovarian stimulation. In three patients, sigmoid endometriosis was diagnosed at laparoscopy for sterility. Because of the absence of digestive symptoms or repercussion on the bowel, no bowel resection was performed before ovarian stimulation. All patients experienced severe digestive symptoms during ovarian stimulation, and a segmental sigmoid resection had to be performed. Analysis of endoscopic and radiological data demonstrated that bowel lesions of small size may rapidly enlarge and become highly symptomatic under ovarian stimulation. At immunohistochemistry, these infiltrating lesions displayed high populations of steroid receptors and a high proliferative index (Ki-67 activity), suggesting a strong dependence on circulating ovarian hormones and a potential for rapid growth under supraphysiological oestrogen concentrations. Clinicians should be aware of this rare but severe digestive complication of ovarian stimulation. The early diagnosis of such lesions may help the patients to avoid months of morbidity falsely attributed to ovarian stimulation side effects. Further experience is necessary to determine the optimal attitude when diagnosing a small and asymptomatic endometriotic bowel lesion before ovarian stimulation.