Background Ulcerative colitis (UC) incidence has bimodal age distribution with a peak in the second to fourth decade and a second smaller peak in the sixth to eighth decade. We assessed the difference in rates of clinical and endoscopic response and remission in adult (≤60 years of age) and elderly (>60 years of age) mild-to-moderate (Mayo Clinic Score ≥5) UC patients treated with mesalazine. Methods We performed a post-hoc analysis of data from a phase 3 non-inferiority trial of 817 UC patients treated with mesalazine for 8 and additional 38 weeks in a double-blind and open label study, respectively (D’Haens et al. Aliment Pharmacol Ther.2017;46:292–302). The differences between groups were analysed using Wilcoxon rank sum or chi-square test with continuity correction. P-value of <0.05 was considered to be statistically significant. Results Elderly patients had longer disease duration, higher body mass index, higher number of co-morbiditities and concomitant medications recorded prior and during the trial, when compared with adults participating in the study (Table 1). These patients also had higher baseline Mayo endoscopic score (2.38±0.486 standard deviation [SD] in elderly vs. 2.26±0.439 SD in adult patients; p-value=0.0077). No difference in rates of combined clinical and endoscopic remission, clinical remission and response, endoscopic remission and response were observed at week 8 and 38 (Table 2). Conclusion We observed similar rates of clinical and endoscopic response and remission in adult and elderly mild-to-moderate UC patients treated with mesalazine for 8 and 38 weeks.