Background The aim of this study was to adapt the 'Sport Fitness Index' into Turkish and to ensure its validity and reliability. Methods After obtaining the necessary permissions, the Sports Fitness Index was independently translated from its English original to Turkish by four different physicians specialising in sports medicine. The content validity of index v.1 was calculated using the Davis technique in sample 1 of 20 people regularly participating in sports. In sample 2 consisting of 104 athletes who had a sports-related ligament/muscle injury or applied to the sports medicine clinic for general medical examination; the validity and reliability of index v.2 were examined. ROC analysis was applied to determine the cut-off point value of the score obtained from the Turkish version of the index. Results The calculated I-CVI (lowest: 0.80, highest: 0.95) and S-CVI/Ave values (0.87) showed that the index provided content validity. Item 1 and item 10 were removed from the Turkish version of the index, as it caused a decrease in the Cronbach's alpha coefficient of the index v.2. Thus, the Cronbach's alpha coefficient of the index was calculated as 0.925. In the Turkish version of index v.2, the single-factor structure (explained variance rate 66.22%; eigenvalue 5.29) was preserved. The index provided confirmatory factor analysis model fit indices. The index provided a high level of negative correlation (r > -.60; P = .0001) with the total score of the Physical Activity Inadequacy Scale Short Form-10 and the sub-scores of all summary components (r > -.60; P = .0001). According to the ROC curve, the best cut-off point was 70 points with 96.6% sensitivity and 75% specificity in the Turkish version of the index. Conclusion The Sports Fitness Index-TR provided its Turkish validity and reliability with its 8-item and single-factor structure. The cut-off point is accepted as 70 points.