In this paper we describe the evaluation of a personalized information system for patients with cancer. Our system dynamically generates hypertext pages that explain treatments, diseases, measurements etc related to the patient's condition, using information in the patient's medical record as the basis for the tailoring. We describe results of a controlled trial comparing this system with a nonpersonalized one. The results of the trial slow significant results concerning the patients' preferences for personalized information. We discuss the implications of our evaluation and results for the development and evaluation of future personalized systems, and adaptive hypertext systems in particular.