Re-injury worry is an important construct in competitive sport that may influence performance and increase the risk of re-injury. However, there are currently no available instruments to measure the causes of re-injury worry. The purpose of this study was to develop the Causes of Re-Injury Worry Questionnaire (CR-IWQ). The study was conducted in three independent research phases to investigate the following: (a) the content relevance, (b) the factor structure and the factorial validity, (c) the concurrent validity, (d) the discriminant validity, and (e) the test-retest reliability (intraclass correlation coefficients; ICC), and the internal consistency of the instrument. Exploratory factor analysis (EFA) was chosen to examine the factor structure of the CR-IWQ. Confirmatory factor analysis (CFA) was used to examine further the factorial validity of the instrument. A number of valid constructs were used to assess the concurrent and discriminant validity of the CR-IWQ. The reliability of the new instrument was examined using Pearson r (ICC) and Cronbach α. Three hundred and seventy athletes with an acute musculoskeletal sport injury in the last year participated in the study. EFA revealed a 12-item model, representing two factors ("Re-injury worry due to rehabilitation" and "Re-injury worry due to opponent's ability"). CFA supported the two-factor model of the CR-IWQ. The concurrent and discriminant validity of the CR-IWQ was confirmed by examining correlations between the CR-IWQ with other constructs. The ICCs and the Cronbach α indices of the CR-IWQ were acceptable. We have demonstrated that the CR-IWQ is a good psychometric instrument that can be used for clinical and research purposes.