Objective: To compare the persistence, retention rate and prescription pattern of original infliximab and infliximab CT-P13 in biologic- naïve patients with ulcerative colitis., Method: This was an ambispective study of biologic-naive patients with ulcerative colitis who received non-simultaneous first-line treatment with Remicade ® (infliximab) and Remsima® (infliximab CT-P13) over a 10-year study period (2012-2021). Data on their age, weight, persistence, retention rate and on whether they required intensification or deintensification throughout the study period was collected. The real patient/year cost of Remicade® and Remsima® was determined individually based on the amounts administered during the study period., Results: 27 biologic-naive patients were treated with Remicade® and 53 with Remsima®. Neither patient group presented with differences in terms of weight and age. Persistence (median ± interquartile range) with Remicade ® was 42.49 ± 57.48 months, as compared to 27.50 ± 58.50 months for Remsima®, without significant differences (p = 0.455). The retention rate at 6, 12, and 24 months was 81%, 63%, and 33%, respectively, for the Remicade® group and 71%, 47%, and 37%, respectively, for the Remsima® group. Nine subjects in the Remicade® group vs 11 patients in the Remsima ® group were intensified. Regarding deintensification, five patients treated with Remicade® were deintensified, as compared with 7 patients on Remsima®. Savings obtained with the use of Remsima® amounted to 203,649 €, which would allow treating an additional 118 patients with biosimilar infliximab for one year., Conclusions: There are no significant differences in persistence, retention, and number of intensifications or deintensifications between iologicnaïve patients treated with Remicade® and those treated with Remsima®, the latter being an effective, safe and economical alternative for the treatment of ulcerative colitis., (Copyright AULA MEDICA EDICIONES 2014. Published by AULA MEDICA. All rights reserved.)