The efficiency of modern health care relies more and more upon a computerised infrastructure. Open distributed IT-systems have started to bring professionals together from all over the world. On the one hand easy processing and communication of images, sounds, and texts will help to represent and treat illnesses and diseases efficiently, on the other hand they may threaten the privacy of patients, and the accountability and professional secrecy of health care professionals. The European Union has initiated a multi disciplinary project to come up with practical guidelines how to achieve a Secure Environment for Information Systems in MEDicine (SEISMED). This project has taken into account the traditional and proven principles of health care data processing, the various data protection legislations within the EU, the enormous and subtle risks of health care information systems, and the cost of changing existing technology. Four Reference Centres in Europe have validated most of the guidelines.