Pentosan polysulfate is used for symptomatic management of interstitial cystitis. At one institution we incidentally noted six patients who were on this agent and had a diagnosis of inflammatory bowel disease (IBD). Three of these patients stopped the drug and all three had clinical and/or endoscopic improvement. Three of the six patients developed multifocal dysplasia. This observation led us to evaluate the hypothesis that pentosan polysulfate is associated with dysplasia in patients with IBD.