Clinical investigation of new therapies generates a tremendous amount of patient information. Much of this information is also used to direct the day to day care of the individual patients. It is imperative that these data be collected in a systematic manner that includes an efficient and flexible quality control mechanism and the ability to rapidly and easily retrieve individual study parameters for specific patients. In addition, statistical analyses must often be performed on subsets of the patient information and the results of these analyses presented in the form of a report. A computerized system that accomplishes each of these goals and several others has been developed at the Memorial Sloan-Kettering Cancer Center. The Clinical Information System is described and examples of its capabilities are presented.