Decision aids (DAs) are increasingly being developed to help patients make shared health care decisions with their practitioners. There are no formal comparisons of the efficacy of different delivery methods. Interactive computerized delivery methods have the advantage of allowing patients control over flow of information and to receive feedback on their comprehension. The purpose of this study was to compare the efficacy of an interactive computerized DA for women considering long-term hormone replacement therapy, to that of a validated audio-booklet version of the same intervention. Fifty-one peri-menopausal women were randomized to use either the computerized or the standard audio-booklet version of the DA. The computerized version presented identical information with the addition of feedback modules to reinforce the participant's understanding. The patients were interviewed with a pre- and post-intervention questionnaire. The computerized DA improved realistic expectations by 52.7% over baseline versus 27.6% with the audio-booklet (P=0.015). Knowledge (Kn) scores improved by 17.5 and 8.4% for the computer and standard DA groups, respectively (P=0.019). The results of this study have implications for future DA design, and other areas where patient Kn and understanding are important, such as in the setting of informed consent.