To summarize the evidence available on the effects of decision aids in surgery. When consenting to treatment, few patients adequately understand their treatment options. To help patients make deliberate treatment choices, decision aids provide evidence-based information on the disease, treatment options, and their associated benefits and harms. Although decision aids are not designed to direct patients toward a particular treatment option, it is possible that their introduction will change the proportion of patients that opt for surgery. We searched electronic databases for studies that evaluated a decision aid in patients offered both surgery and alternative treatment options, regarding the effect on the actual treatment choices made. In addition, we documented effects on knowledge, decisional conflict, anxiety, quality of life, patient involvement, satisfaction, mortality, morbidity, and costs. Seventeen studies were included. Overall, methodological study quality was good. Patients in the decision aid group less often chose to undergo invasive treatment [risk ratio = 0.80; 95% confidence interval, 0.67-0.95), had more knowledge about treatment options [mean difference = 8.99; 95% confidence interval, 3.20-14.78), and experienced less decisional conflict (mean difference = -5.04; 95% confidence interval, -7.10 to -2.99). Levels of anxiety and quality of life were similar. Offering a decision aid increases the number of patients who prefer conservative or less invasive treatment options. As decision aids improve patient knowledge and lower decisional conflict without raising anxiety levels, they have a place in surgery to help surgeons and patients achieve well-considered and shared treatment decisions.