The article describes the development of AMSTAR, a measurement tool designed to assess the methodological quality of systematic reviews. The tool was developed by combining items from existing instruments and adding new items based on recent empirical evidence and expert consensus. A 37-item assessment tool was created and applied to 99 paper-based and 52 electronic systematic reviews. Exploratory factor analysis identified 11 underlying components, which were further reduced to 11 items through a nominal group technique involving methodological experts. The resulting AMSTAR tool has good face and content validity for measuring the methodological quality of systematic reviews. However, additional studies are needed to validate its reproducibility and construct validity before strong recommendations can be made for its use.The article describes the development of AMSTAR, a measurement tool designed to assess the methodological quality of systematic reviews. The tool was developed by combining items from existing instruments and adding new items based on recent empirical evidence and expert consensus. A 37-item assessment tool was created and applied to 99 paper-based and 52 electronic systematic reviews. Exploratory factor analysis identified 11 underlying components, which were further reduced to 11 items through a nominal group technique involving methodological experts. The resulting AMSTAR tool has good face and content validity for measuring the methodological quality of systematic reviews. However, additional studies are needed to validate its reproducibility and construct validity before strong recommendations can be made for its use.