As the book title already indicates, this diploma thesis concerns itself with the question of how medical treatment of Jehovah's Witnesses and their self-determined, religiously-motivated decision to refuse blood transfusions can cause legal problems. With regard to the procedural method, emphasis is put on the doctor-patient relationship. Furthermore, the religious background of the faith commandement will shed light on, as discussed on medical-ethical approaches. Separately, the situation of minors is also shown, where the medical treatment takes place between the foreign regulation on the part of parents and their own self-determination, and this situation leading to the issue of granting consent. Finally, personal concluding remarks follow, which includes an additional summary of the issues raised.