We present the case of a 36-year-old woman who presented to our clinic for a second opinion. After multiple previous surgeries, she presented with an abdominal wound infection, which was initially treated conservatively. In the further course, catamenial bleeding occurred as an unusual symptom, and the suspicion of a fistula formation was postulated. Subsequent surgical repair and consecutive histopathological diagnosis revealed evidence of a fistula with endometriosis genitalis externa and thus gave an explanation for this striking clinical case presentation.