Objective: The objective of this study was to evaluate the effects of the decision support tool (DST) on the assessment of the acutely ill or injured out-of-hospital patient. Methods: This study included systematic reviews of randomized controlled trials (RCT) where the DST was compared to usual care in and out of the hospital setting. The databases scanned include: (1) Cochrane Reviews (up to January 2010); (2) Cochrane Controlled Clinical Trials (1979 to January 2010); (3) Cinahl (1986 to January 2010); and (4) Pubmed/ Medline (1926 to January 2010). In addition, information was gathered from related magazines, prehospital home pages, databases for theses, conferences, grey literature and ongoing trials. Results: Use of the DST in prehospital care may have the possibility to decrease “time to definitive care” and improve diagnostic accuracy among prehospital personnel, but more studies are needed. Conclusions: The amount of data in this review is too small to be able to draw any reliable conclusions about the impact of the use of the DST on prehospital care. The research in this review indicates that there are very few RCTs that evaluate the use of the DST in prehospital care.