The Team Decision Making Questionnaire (TDMQ) demonstrated internal consistency, stability over time, and construct validity. Internal consistencies were excellent and Cronbach's Alphas (N = 102) for the 4 components ranged from 0.83 to 0.91. The internal consistency for the total instrument was 0.96. Test re-test reliability (N = 22) measured with Intraclass Correlation Coefficient was good. Transdisciplinary teamwork is widely practiced in health care. However, specific measures to evaluate transdisciplinary team decision-making are not described in the literature. The purpose of this study was to develop and psychometrically test a scale to measure the quality of transdisciplinary teamwork. A multi-method approach using focus groups, field testing, and quantitative instrument development procedures was used to develop and evaluate TDMQ. Principal component analysis (PCA) with a varimax rotation (N = 102) revealed a four-component solution resulting in a 19-item measure consisting of 4 subscales including Decision Making, Team Support, Learning, and Developing Quality Services. This study's findings support the use of the TDMQ for measuring the benefits of transdisciplinary teamwork. The four subscales of the measure provide insight into the nature of such benefits. To validate the TDMQ research is required with a greater number of health care professionals and in other clinical fields.