This paper reports the development of a scale for assessing the quality of reports of randomised controlled trials for psychological treatments. The Delphi method was used in which a panel of 15-12 experts generated statements relating to treatment and design components of trials. After three rounds, statements with high consensus agreement were reviewed by a second expert panel and rewritten as a scale. Evidence to support the reliability and validity of the scale is reported. Three expert and five novice raters assessed sets of 31 and 25 published trials to establish scale reliability (ICC ranges from 0.91 to 0.41 for experts and novices, respectively) and item reliability (Kappa and inter-rater agreement). The total scale score discriminated between trials globally judged as good and poor by experts, and trial quality was shown to be a function of year of publication. Uses for the scale are suggested.