Background Internet-delivered trauma-focused cognitive behavioural therapy is efficacious for PTSD; however, no studies have investigated the roles of individual treatment components or the safety of online treatments. Aims To compare the efficacy and safety of an online treatment for PTSD comprised of psychoeducation, stress management, cognitive restructuring and exposure components with the equivalent protocol without the exposure components, using a randomised controlled trial design. Methods Sixty-six individuals were randomised to a non-exposure condition and 59 to the full protocol with exposure components. Treatment duration was 8 weeks and pre-, post-treatment and three-month follow-up outcomes were analysed using a mixed linear modelling approach. Results Both groups achieved improvements in symptoms with no differences between groups on any primary or secondary outcome measures, diagnostic remission rates or adverse events. Limitations The study included several secondary measures that have not been previously validated and treatments were not time matched in terms of number of lessons. Conclusions These findings indicate that trauma-focused cognitive behavioural therapy for PTSD with or without exposure components can be safe and efficacious.