Comprehensive Behavioral Intervention for Tics (CBIT) is considered a first-line therapy for tics. However, availability of CBIT is extremely limited due to a lack of qualified therapists. This study is a multicenter (n = 5), randomized, controlled, observer-blind trial including 161 adult patients with chronic tic disorders (CTD) to provide data on efficacy and safety of an internet-delivered, completely therapist-independent CBIT intervention (iCBIT Minddistrict®) in the treatment of tics compared to placebo and face-to-face (f2f) CBIT. Using a linear mixed model with the change to baseline of Yale Global Tic Severity Scale-Total Tic Score (YGTSS-TTS) as a dependent variable, we found a clear trend towards significance for superiority of iCBIT (n = 67) over placebo (n = 70) (−1.28 (−2.58; 0.01); p = 0.053). In addition, the difference in tic reduction between iCBIT and placebo increased, resulting in a significant difference 3 (−2.25 (−3.75; −0.75), p = 0.003) and 6 months (−2.71 (−4.27; −1.16), p < 0.001) after the end of treatment. Key secondary analysis indicated non-inferiority of iCBIT in comparison to f2f CBIT (n = 24). No safety signals were detected. Although the primary endpoint was narrowly missed, it is strongly suggested that iCBIT is superior compared to placebo. Remarkably, treatment effects of iCBIT even increased over time.