This paper introduces the teleradiology system, MEDICUS, which has been developed at the Deutsches Krebsforschungszentrum (German Cancer Research Center) in Heidelberg, Germany. The system is designed to work on ISDN lines as well as in a local area network. The global software architecture is explained in the article. Special attention has been given to the design of the user interface and data security, integrity and authentication. The software has been evaluated in a German field test at 13 radiology departments in university clinics, small hospitals, private practices and research institutes. More than 30 thousand images have been transmitted using this system during a 9 month period. Realized application scenarios are: in-house communication, image and report delivery to referring hospitals, remote reporting, radiotherapy treatment planning and research cooperation. Experience has shown that the system is easy to use and saves time. It obviates the need for patient transport and reduces film costs. Experiences of individuals while using the system during the field test helped define the functionality of the second generation teleradiology system which is even more flexible and is also available as a commercial product.