An internet-delivered cognitive behavioral treatment (ICBT) based on systematic exposure exercises has previously shown beneficial effects for patients with irritable bowel syndrome (IBS). Exposure exercises may be perceived as difficult for patients to perform because of the elicited short-term distress and clinicians may be reluctant to use these interventions. The aim of this study was to compare ICBT with the same protocol without systematic exposure (ICBT-WE) to assess if exposure had any incremental value. This randomized controlled dismantling study included 309 participants diagnosed with IBS. The treatment interventions lasted for 10 weeks and included online therapist contact. ICBT-WE comprised mindfulness, work with life values, acceptance, and encouraged reduced avoidance behaviors, while ICBT also included systematic exposure to IBS symptoms and related situations. Severity of IBS symptoms was measured with the Gastrointestinal Symptom Rating Scale - IBS version (GSRS-IBS). The between-group Cohen's d on GSRS-IBS was 0.47 (95% CI: 0.23-0.70) at post-treatment and 0.48 (95% CI: 0.20-0.76) at 6-month follow-up, favoring ICBT. We conclude that the systematic exposure included in the ICBT protocol has incremental effects over the other components in the protocol. This study provides evidence for the utility of exposure exercises in psychological treatments for IBS.