Interstitial cystitis/bladder pain syndrome (IC/BPS) has debilitating symptoms and results in a poor quality of life. This study investigated the associations between demographic and clinical factors and symptom severity in patients with IC/BPS in Taiwan.Patients with documented IC/BPS refractory to conventional treatments from 2007 to 2009 were enrolled. Sociodemographic data and a medical history were obtained. Clinical assessments were performed using the O'Leary–Sant IC symptom index (ICSI) and problem index (ICPI), visual analog scale of bladder pain, and global response assessment to treatment. Patients kept a 3-day voiding diary of daytime and nighttime frequency, and functional bladder capacity (FBC) and uroflowmetry parameters (maximum flow rate, voided volume, and postvoid residual) were measured. Univariate and multivariate analyses were used to evaluate the associations between demographic/clinical factors and symptom severity.A total of 80 patients (75 women and 5 men) were enrolled. On univariate and multivariate analysis, the characteristics most associated with worse ICSI, ICPI, pain score, daytime frequency and nocturia episodes, and FBC were maximum bladder capacity (MBC) under anesthesia, duration of symptoms, body mass index (BMI), and employment status.MBC and duration of symptoms were predictive factors of symptom severity in patients with refractory IC/BPS. BMI and employment status were also found to be associated with symptom severity in these patients.