The aim of this study was to develop a quality of study tool to rates the methodological quality of individual primary randomized controlled trials (RCT) to be included in a meta-analysis. A Delphi-technique using several rounds of questions to seek consensus, among trialists, on criteria important in a RCT was used. Eight trialists formed the Delphi panel. The developed quality of study tool consisted of 53 items in 15 dimensions. The tool was tested for reliability and validity. Unlike many other quality assessment tools, the developed tool may be used to rate numerically each primary study. This is important in reviews or in meta-analyses where one objectives may be to ascertain whether those studies of a higher quality exhibit different results to reviewing studies of lower quality. The tool needs further testing.