Increased interest in health care consumerism has created an environment conducive to growth in the use of decision aids (DAs) to support patient decision making. The authors review the research literature published within the past 5 years that assesses the effects of DAs in the areas of screening and treatment. Multiple measures are used to evaluate the effectiveness of DAs, with mixed evidence of impacts. To date, most evidence from screening studies suggests that DAs are effective in increasing knowledge and are acceptable to patients, but patient uptake of screening has been mixed. Among treatment studies, there is some, but limited, evidence showing impact of DAs on immediate and long-term decisional conflict, patient satisfaction, and quality of life. Few studies provide assessment of impact on health outcomes, quality of care, utilization, or costs, all areas likely to be of growing interest to private purchasers, insurers, and public programs.