BACKGROUND AND OBJECTIVE: The influence of concomitant prednisolone on clinical outcomes and safety in infliximab-treated ulcerative colitis (UC) patients is unknown. DESIGN, SETTING, PARTICIPANTS AND OUTCOME MEASURES: A retrospective cohort study was performed, including 147 UC patients treated with infliximab at a tertiary inflammatory bowel disease (IBD) centre. Primary outcome was corticosteroid-free clinical remission (CFCR) at week 14 and week 52. Patients were grouped according to prednisolone tapering regimens: standard (</=5 mg/week), fast (>5 mg/week), direct discontinuation or no prednisolone. Patients intolerant to corticosteroids and patients stopping corticosteroids in preparation for surgery including colectomy during their initial admission were excluded. RESULTS: There was no overall association between prednisolone exposure or no exposure and CFCR at weeks 14 or 52 of infliximab. The proportion of patients with C reactive protein </=5 mg/L was higher in the standard tapering at week 14 as compared with faster regimens or no prednisolone. In subgroup analyses, the standard tapering was associated with a higher rate of CFCR at week 14 compared with the fast-tapering regimen in patients receiving >/=40 mg prednisolone at initiation of infliximab (64.3% vs 26.3%, p=0.04) and among patients admitted with acute severe UC (66.6% vs 23.5%, p<0.05). Similar data were seen at week 52. Prednisolone did not affect infliximab trough levels but increased infection rates (10/77 vs 2/70, p=0.03), in particular C. difficile infection. CONCLUSION: In UC patients with limited disease burden, prednisolone did not affect effectiveness of infliximab. However, patients with increased disease burden seem to benefit from corticosteroid combination therapy.