Introduction: Hand osteoarthritis (HOA) is a prevalent rheumatic disease that may cause significant disability. The Functional index for HOA (FIHOA) is a validated questionnaire to evaluate loss of function in patients with HOA. Objective: To undertake a cross-cultural adaptation and validation of FIHOA into Portuguese. Patients and methods: First, the original French version of FIHOA had been forward-backward translated into Portuguese, according to the guidelines for cross-cultural adaptation. Secondly, patients with primary HOA were consecutively recruited in three Portuguese rheumatology outpatient clinics between May 2016 and April 2018. The final consensual Portuguese version of FIHOA was administered to 52 patients. A numerical rating scale (NRS – 0 to 100mm) for hand pain and for perceived hand dysfunction was also registered. Ten randomly selected patients were re-administered the same tools 5 to 15 days later. Internal consistency, test-retest reliability, internal construct validity and external validity related to dysfunction NRS were evaluated. Results: Fifty-two patients were evaluated: all right-handed, 96% women, mean age of 63 (10) years and 8 (6) years of disease duration. Mean (SD) pain and dysfunction were 47 (25) and 46 (25), respectively, with 68% patients being symptomatic. Mean (SD) FIHOA was 7 (5). Cronbach’s alpha for internal consistency was high and adequate (0.87) and corrected item-total correlation revealed adequate performance. For reliability, Spearman’s rho coefficient was 0.88 and total intraclass correlation coefficient (ICC) between test and retest was 0.87, showing good reliability. Factor analysis revealed three factors accounting for 71% of the variance of the score, with the first one (including questions 1, 2, 3 and 10) being responsible for 47% of the variance. Spearman’s rho between FIHOA and dysfunction NRS was 0.5, showing a moderate but significant correlation and moderate external validity. Conclusion: The Portuguese version of FIHOA is a consistent, reliable, and valid instrument to measure loss of function in HOA Portuguese patients.