Objective: The aim of this study is to investigate whether the Big Five personality traits predict the outcome of Internet-based cognitive behavioural therapy (ICBT) and whether they moderate the outcome between ICBT and face-to-face group cognitive behavioural therapy (GCBT). Design: This study investigated the Big Five personality traits as predictors and moderators of the outcome (tinnitus handicap) in a trial comparing ICBT and GCBT for chronic tinnitus. Study sample: N= 84 patients with chronic tinnitus were randomised to either ICBT (n = 41) or GCBT (n = 43). Results: A multilevel model for discontinuous change was performed. Higher scores on the "openness" scale of the Big Five Personality inventory (BFI-10) predicted a lower tinnitus handicap (Tinnitus Handicap Inventory, THI) at post-treatment in ICBT (p amp;lt;0.05). Openness moderated the outcome at post-treatment in favour of ICBT (p amp;lt;0.05). Higher scores on the BFI-10 "conscientiousness" scale predicted a more favourable outcome in ICBT at 6-month (p amp;lt;0.05) and 12-month follow-up (pamp;lt; 0.05), but the BFI-10 "conscientiousness" scale was positively associated with the THI at baseline (pamp;lt;0.05). Conclusions: ICBT might be the preferred treatment choice for tinnitus patients being open towards new experiences. Moreover, ICBT requires autonomous work and self-motivation by the patient in order to have an impact.