Telemedicine is changing the classical form of health care delivery, by providing efficient solutions to an increasing number of new situations: here we consider those which require some type of computer-supported cooperative work (CSCW) between health care professionals located in different clinical sites. This paper presents the design and development of a telemedicine system for remote computer-supported cooperative medical imaging diagnosis. The main and novel component of our system is a new CSCW distributed architecture, comprised by a collaborative toolkit to add audioconferencing, telepointing, window sharing, user's coordination and application synchronization facilities, either to existing or new medical imaging diagnosis applications. In comparison with existing CSCW products, mainly based on centralized architectures, our distributed toolkit is specially designed for telemedicine applications: to allow different levels of sharing between participants, to improve user feedback in highly interactive user interfaces, and to optimize the required communication bandwidth in order to implement a telemedicine CSCW application on almost any telecommunication network. This telemedicine CSCW system has been applied to build a cooperative medical imaging diagnosis application, in which two doctors, located in different hospitals, need to achieve a cooperative diagnosis on haemodynamic studies using cardiac angiography images. The design of the graphical user interface for this kind of telemedicine CSCW systems, a critical component which conforms any telemedicine application, is also addressed with a new methodological approach, to assure the system usability and final user acceptance. The telemedicine cardiac angiography pilot has been implemented, tested and evaluated within the Research Project 'FEST-Framework for European Services in Telemedicine' funded by EU AIM Programme.