Background: Several studies show that psychological treatments relieve symptoms for patients suffering from irritable bowel syndrome (IBS). However, there are no consistent findings that show what patient characteristics make a psychological treatment more or less likely to result in improvement. We have previously conducted a study of a newly developed internet-delivered cognitive behavioral therapy (ICBT) that emphasized exposure to IBS symptoms and IBS-related situations and reduced symptom-related avoidance. The study showed that the treatment led to improvement in IBS symptoms compared to a waiting list and that treatment gains were maintained over a 15-18 month follow-up period. The aim of the present study was to investigate several possible predictors of short-and long-term treatment outcome in terms of symptom improvement, based on data collected in the previously conducted treatment trial. less thanbrgreater than less thanbrgreater thanMethods: Demographics, comorbid psychological distress, IBS-related fear and avoidance behaviors, and IBS-related disability were investigated as predictors of treatment outcome in the sample consisting of 79 participants diagnosed with IBS who had undergone 10 weeks of ICBT. Predictors that were significantly correlated with symptom levels at post-treatment and follow-up were entered into multiple regression analyses that controlled for pre-treatment symptom levels. less thanbrgreater than less thanbrgreater thanResults: There were measures within each domain, i.e., comorbid psychological distress, IBS-related fear and avoidance behaviors, and IBS-related disability, with the exception of demographic data, that were correlated with the symptom levels at post-treatment and follow-up. However, when these were entered into a multiple regression analyses that controlled for pre-treatment levels, none remained a significant predictor of the post-treatment and follow-up symptomatic status. less thanbrgreater than less thanbrgreater thanConclusions: The study did not find any individual characteristics that made patients more or less likely to respond to the exposure-based ICBT. The finding that comorbid psychological distress did not predict outcome is in accordance with previous studies. Reliable predictors for response to any type of psychological treatment for IBS remain to be established.