Objective: The objectives of this study were to translate into Spanish, cross-culturally adapt and validate the TFI. Materials and Methods: The TFI questionnaire translated into Spanish (Sp-TFI) and cross-culturally adapted following the published guidelines on cross-cultural adaptation of health questionnaires was evaluated using two indicators. Its internal consistency was assessed with Cronbach’s α considering the Tinnitus Handicap Inventory (THI) as the gold standard. Further, its test-retest reliability was assessed with intraclass correlation coefficients (ICCs). ICCs were also calculated for the THI and visual analogue scales (VAS) for tinnitus tested and retested in all participants. Results: The mean age of the 18 participants was 45.77 (SD: 11.87) years; 12 were female (66.67 %) and 6 were male (33.33%). Half of the participants experienced tinnitus in their left ear and half in their right. The mean pure-tone average (PTA) in the affected ear was 29.34 (SD: 8.08) dB-HL. Regarding internal consistency and reliability of the Sp-TFI respectively, Cronbach’s α was 0.83 and the ICC type (2,1) was 1 (CI: 0.99–1). Among the variables studied, we found the following independent predictors had statistically significant effects on THI score: sex (p < 0.01), PTA (p = 0.03), overall Sp-TFI score (p = 0.02) and Sp-TFI SL, R and A subscale scores (p = 0.03, p = 0.03, and p < 0.01, respectively). Conclusion: Based on the internal consistency and reliability results obtained in this study, the cross-culturally adapted Spanish version of the TFI (Sp-TFI) has been validated for use in Spain. Cite as: Maria Montserrat Soriano-Reixach, Jorge Rey Martinez, Juan Jose Navarro Sampedro, et al. Translation into Spanish and validation of the Tinnitus Functional Index. Authorea. August 09, 2022.DOI: 10.22541/au.166004572.24057118/v1