The aim of this study was to examine the relationships between irritable bowel syndrome (IBS)-specific behaviours, catastrophizing, anxiety sensitivity, positive mood and aspects of suffering, as well as to investigate possible mediating effects of catastrophizing, anxiety sensitivity and positive mood on relationships between specific behaviours and aspects of suffering. The research was conducted as a part of the scientific project "Cognitive-affective and behavioural determinants of irritable bowel syndrome". 74 subjects (60 women and 14 men) diagnosed with IBS participated in research, with ages ranging from 21 to 80 years. The study was conducted in three stages - the first and third stage consisted of completing various questionnaires in hospitals, while the second stage consisted of a two-week monitoring period using a diary technique. Results showed a negative correlation between self-illness separation and illness perception measure. Results also showed a negative correlation between IBS-specific behaviours and self-illness separation, as well as a positive correlation between specific behaviours and illness perception measure. Specific behaviours are also positively correlated with both catastrophizing and anxiety sensitivity. Catastrophizing and anxiety sensitivity are positively correlated, while positive mood is significantly negatively correlated with catastrophizing and negatively with illness perception measure. Catastrophizing and anxiety sensitivity are negatively correlated with self-illness separation, and positively with illness perception measure. Furthermore, catastrophizing and anxiety sensitivity do not mediate the relationship between avoidance behaviours and self-illness separation, but they do significantly mediate the negative relationship between control behaviours and self-illness separation. In addition, catastrophizing and anxiety sensitivity mediate the positive relationship between avoidance behaviours, as well as control behaviours and illness perception measure. The findings of this study contribute to the explanation of IBS from a biopsychosocial perspective, ie the CBT model, indicating the importance of roles of IBS-specific behaviours, catastrophizing and anxiety sensitivity in the suffering of patients.