Background: Inflammation is a known pitfall of surveillance colonoscopy for inflammatory bowel disease (IBD) as it is difficult to differentiate between inflammation and true dysplasia. This randomized controlled trial assessed the effectiveness of a low dose of corticosteroids prior to surveillance colonoscopy to decrease mucosal inflammation. Methods: IBD-patients scheduled for surveillance colonoscopy between July 2008 January 2010 were eligible to participate. Patients were randomized to either two weeks daily 20 mg prednisone and calcium plus vitamin D prior to surveillance colonoscopy or no treatment. All biopsies were reviewed by an expert gastrointestinal pathologist who was blinded for medication-use. Statistics were performed using chi-square tests, non-parametric tests and binary logistic regression. Results: Sixty patients (M/F 30/30, UC/CD 31/29) participated: 31(52%) in the treatment arm and 29 (48%) in the control group. In the treatment arm, 247 biopsies were scored against 262 in the control group. In the treatment arm 27 out of 247 biopsies (10.9%) had a score >1 on the Geboes scale, against 50 out of 262 biopsies (19.1%) in the control group, p = 0.013. In total, 58% of the treatment arm against 66% of the control group had endoscopic or histological mucosal inflammation (p = 0.6). There was a trend for patients in the treatment arm to have less severe inflammation compared with the control group, however this was not significant (p = 0.12). Conclusions: In our cohort, a short course of corticosteroids decreases the overall histological disease activity in individual biopsies without major side-effects. Moreover, there is a trend for corticosteroids to decrease the maximum severity of both endoscopic and histological disease activity per patient. (C) 2010 European Crohn's and Colitis Organisation. Published by Elsevier B.V. All rights reserved.