Over recent years, many scholars have studied the conceptual modeling of information systems based on a model of representation formulated by Wand and Weber. This model offers a set of premises about representational deficiencies and their implications for development and use of conceptual modeling in IS practice. Yet, only few examples of empirical research exist. One of the related problems is the lack of validated measurement instruments that could be used in such studies. This paper reports on the development of a valid and reliable instrument for measuring the perceptions that individuals have of the representational deficiencies of conceptual modeling artifacts. We describe a multi-stage approach for instrument development that incorporates feedback from expert and user perspectives. We also report on a field test of the instrument with modeling practitioners. The resulting instrument can be used in future studies that investigate the use of conceptual modeling in IS practice.