 Background and objectives. So-called prediction rules risk scores have become increasingly popular in all medical disciplines. This will only rise with the introduction of electronic patient records as these will enhance their use. However, effects of implementation of such rules in daily care has hardly been studied. Also not in anesthesiology. We developed and validated an accurate rule to preoperatively predict the risk of postoperative nausea and vomiting PONV in surgical inpatients. PONV causes extreme patient discomfort and occurs in even 30-50 of all surgical inpatients. As routine administration of PONV prophylaxis is not cost-effective, a risk-tailored approach using an accurate prediction rule is widely advocated. Before large-scale implementation, we aim to study whether such implementation indeed changes physician behavior and improves patient outcome. Given the increase interest in prediction rules, another aim is to study general causes of successfulpoor implementation of prediction rules in health care. Design. Cluster, randomized study in which 60 anesthesiologists and senior residents of the UMC Utrecht will be randomized to either the intervention or usual care group. 