Cognitive behaviour therapy (CBT) can reduce tinnitus distress but is not available for most patients. Therapist guided, internet-based CBT (ICBT) increase availability and has been shown to be effective. However, the initial positive results need to be replicated in larger samples, and treatment dropout has not been thoroughly studied. Moreover, it has not been evaluated if a low-intensity version of ICBT without therapist contact could be an alternative for patients who do not need or are able to manage the full ICBT-program. This study evaluated two parallel interventions delivered in regular care: ICBT for tinnitus distress (n = 293) and a low-intensity version of ICBT (n = 81) for patients with lower levels of tinnitus distress. We also explored predictors of dropout from ICBT and if dropout influences outcome. Tinnitus Reaction Questionnaire (Wilson, Henry, Bowen, & Haralambous, 1991) was used as the primary outcome. Secondary outcomes were measures of depression, anxiety, sleep, and sound sensitivity. Significant reductions following ICBT were found on all measures after treatment and also at a three-month follow-up. Patients receiving low-intensity ICBT showed a significant reduction in distress, even when they had low levels of distress initially. Treatment dropout was preceded by an increase in days spent at each treatment step but not by an increased distress. Early dropout was related to worse outcome. ICBT can be used in a regular clinical setting to reduce tinnitus distress. Early dropouts may need additional management. For help-seeking patients with lower distress, a low-intensity version of ICBT can be used.