Radiology information systems (RIS) have developed over the past 20 years as a specialized area of medical informatics. Although an increasing number of radiology departments utilize such systems, the majority do not. Perhaps this is because no commercially available system has yet demonstrated its ability to provide cost-effective solutions to the diverse problems of different departments. This review begins with a brief history of RIS to point out some approaches that have proven successful and some that have not. Learning about the historical development of RIS also helps understand many of the features that are found in current systems. The bulk of the article is devoted to a detailed discussion of the functional modules found in RIS, including patient registration and data base management, examination scheduling, process control, film file management, diagnostic reporting, financial packages, and management statistics. These discussions emphasize the wide range of activities and problems found in different radiology departments and the wide range of techniques utilized by RIS. General issues of designing or selecting, installing, operating, and optimizing a RIS are discussed briefly. A final section points out areas for future development and expansion of RIS, giving special attention to the incorporation of digital image information into overall radiology systems.