To evaluate disease perception in a cohort of patients with interstitial cystitis/painful bladder syndrome (IC/PBS) using the Brief Illness Perception-Questionnaire (BIP-Q) and to evaluate how this might relate to disease severity. The study is a cross-sectional survey amongst members of Bladder Health UK who had previously received a clinical diagnosis of IC/PBS. A hyperlink containing the questionnaire was sent to the patient group's website and interested members accessed and completed the survey. Participants' inclusion was based on a prior clinical diagnosis of IC/PBS, current O'Leary Sant scores supportive of the diagnosis, and age between 18 and 80. A sample size of 171 was used in the study. The Brief Illness Perception Questionnaire (BIP-Q) and the O'Leary/Sant symptoms and problem indices questionnaire were used to collect data. A multivariable logistic regression analysis was used to test the relationship between items of BIP-Q and severity of IC/PBS. Content analysis was used for the causal domain and subsequently analysed as percentages. Six hundred and one members accessed the questionnaire of whom 159 returned completed questionnaires. One hundred and twenty-two of 159 (≥75%) respondents believe that their illness will continue indefinitely. The majority of the respondents indicated that IC/PBS had a negative impact on their daily lives, caused them worry and made them emotionally unstable. Of the 8 BIP-Q items, those most predictive of disease severity were (adjusted odd ratio and confidence intervals): consequence 0.094 (0.023-0.386); treatment control 2.702 (1.256-5.812); identity 0.141 (0.033-0.600); concern 9.363 (1.521-57.632). Our findings show that IC/PBS negatively impacts participant's quality of life and emotional wellbeing. Higher expectation for treatment benefit and increasing levels of patient concern are predictive for severity of IC/PBS.