Matching individuals to multisite cooperative clinical trials can be a complex and nonintuitive decision process that expends considerable time and may be prone to errors. We developed and tested a web-based decision support tool to aid investigators in matching patients to open clinical trials for children with rhabdomyosarcoma in the context of an international cooperative cancer clinical trials network. A decision tree for trial eligibility based on eight clinical variables representing major disease characteristics was translated into a web-based format. In a blinded fashion, we assessed the accuracy of the tool in assigning 100 randomly selected cases to the proper clinical trial. The web-based tool assigned patients to the proper clinical trial in all 100 randomly selected cases. The time needed to enter data and receive results using this tool is about 1 minute per patient entered. It is feasible to develop a web-based tool to help investigators in matching patients to clinical trials. When such decisions are complex and nonintuitive, such tools have the potential to improve the accuracy of clinical trial assignment and save time.