Introduction: Headache-related disability is influenced by attack frequency, intensity, and duration, but these do not fully capture the impact of headache on a person's life. The Headache Impact Test - 6 questionnaire is widely used, but the psychometric properties of its Italian version (HIT-6_IT) remain untested. This study evaluates the reliability and validity of the HIT-6_IT in people with migraine and tension-type headache. Materials and methods: For reliability evaluation, 55 stable participants with migraine or tension-type headache completed the HIT-6_IT twice, 14 days apart. A separate cohort of 110 participants from the same population was assessed to evaluate the validity of the scale, considering headache type, frequency, intensity, and HIT-6 scores. Reliability was measured by Cronbach's alpha, Intraclass Correlation Coefficient (ICC2,1), and Minimal Detectable Change 95% (MDC95). Construct validity was tested via correlations and subgroup comparisons. Results: HIT-6_IT showed excellent reliability (alpha = 0.77; ICC2,1 = 0.97; MDC95 = 2.52). Scores correlated with headache frequency (r = 0.36) and intensity (r = 0.30), differing significantly between diagnostic subgroups (p < 0.001), supporting the validity of the questionnaire. Discussion: HIT-6_IT is a reliable and valid tool for assessing the impact of migraine and tension-type headache, in both clinical and research settings.
