The potential use of prognostic indices (Pls) as instruments for assessing patient outcome has not met the expectatives associated with their development. The inaccuracy of prognosis evaluations, and the fact that they were designed for groups rather than individual patients, has limited their practical clinical use. Physicians are disappointed that the effort spent in developing these instruments has not been matched by guidance in their proper use. This paper responds to this concern by reviewing the possibilities of Pls. Outcome assessments, with their wide limitations, are still the most frequent use of Pls (although their results should be interpreted with caution). These tools are best used as managerial instruments or quality-control aids. Their effectiveness and efficiency are closely related to the information obtained from Pls. The capability of Pls to define different arms of clinical trials has opened a new field for their use as research cooperative tools. Finally, we review trends for further research.