The representation of patient information for use in clinical workstations is a complex problem. Ideally, it should be addressed in a way that allows multiple uses of the data, including simple manual review, sharing and pooling across institutions, and as input to knowledge-based decision support systems. To a great extent, this means coding information with controlled medical vocabularies, but it does not mean that all information must be codable before workstations are feasible. This paper defines some of the choices, both current and future, that are available to address the needs of controlled medical vocabularies for representing data and knowledge in clinical workstations and explores some of the implications of those choices. © 1994.