BackgroundAmbiguity is inherent to the medical field; hence, assessing and educating medical trainees regarding ambiguity tolerance is essential. The Tolerance of Ambiguity in Medical Students and Doctors (TAMSAD) scale—a novel instrument that assesses ambiguity tolerance in clinical settings—has been widely used for medical education research in Western countries. However, a version of this scale applicable to the intricate clinical contexts of Japan has not yet been developed. In this study, we developed the Japanese version of the TAMSAD (J-TAMSAD) scale and tested its psychometric properties.MethodsIn this multicenter study, we collected data through a cross-sectional survey in two universities (medical students) and ten hospitals (residents) across Japan, and evaluated the structural validity, criterion-related validity, and internal consistency reliability of the J-TAMSAD scale.ResultsWe analyzed the data of 247 participants. The sample was randomly divided in half, with exploratory factor analysis (EFA) performed on one half and confirmatory factor analysis (CFA) on the other. EFA led to an 18-item J-TAMSAD scale comprising five factors. CFA showed acceptable fit for this five-factor model (comparative fit index = 0.900, root mean square error of approximation = 0.050, standardized root mean square residual = 0.069, goodness of fit index = 0.987). There was a positive correlation between the J-TAMSAD scale scores and total reverse scores on the Japanese version of the Short Intolerance of Uncertainty Scale (Pearson correlation coefficient 0.41). The internal consistency was found to be satisfactory (Cronbach’s alpha 0.70).ConclusionsThe J-TAMSAD scale was developed, and its psychometric properties were confirmed. The instrument can be useful for assessing tolerance of ambiguity among medical trainees in Japan. With further validation, it could be used to verify the educational effectiveness of curricula that foster ambiguity tolerance in medical trainees, or even in research assessing the relationship with other variables.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12909-023-04391-1.