Thought-shape fusion (TSF) describes the experience of marked concerns about body weight/shape, feelings of fatness, the perception of weight gain, and the impression of moral wrongdoing after thinking about eating fattening/forbidden foods. This study sets out to evaluate the short version of the TSF trait questionnaire (TSF). The sample consists of 315 healthy control women, 244 women with clinical and subthreshold eating disorders, and 113 women with mixed mental disorders (mixed). The factor structure of the TSF questionnaire was examined using exploratory and subsequent confirmatory factor analyses. The questionnaire distinguishes between a Concept scale and a Clinical Impact scale. However, a lack of measurement invariances refers to significant differences between groups in terms of factor loadings, thresholds, and residuals, which questions cross-group validity. Results indicate that the concept is understood differently in the 3 groups and refers to the suitability of the questionnaire primarily for individuals presenting with symptoms of eating disorders.