Introduction: Because there are very few studies of the use of azathioprine (AZA) for treatment of ulcerative colitis, and most are more than a decade old, we need to establish the efficacy of AZA in our environment for patients who have responded inadequately to steroids. Objective: The objective of this study is to eva- luate short and long term clinical responses to AZA by ulcerative colitis patients in our population who have had inadequate responses to treatment with steroids. Materials and Methods: This is a retrospective study based on a database review of the medical records of 215 ulcerative colitis patients treated at the Hospital Pablo Tobon Uribe between August 2001 and May 2014. Sixty-nine patients (32%) had received AZA, and 30 patients had received at least 3 months of treatment with AZA at the optimal dose of at least 2.0 mg/kg after having responded inadequately to treatment with steroids. This group was included in the study. Results: The median follow-up time was 20 months with a range from three months to 72 months. After three months of treatment, clinical remission was found in 17 patients (57%) out of 30 patients, and partial responses were found in 12 out of 30 subjects (40%). A year after the initial follow-up, 16 patients (53%) maintained clinical remission, three (10%) continued to have partial responses, and five (17%) had relapsed and had received biological therapy. Sixteen patients (53%) achieved one year with steroid treatment suspended and no patients required colectomies. Conclusions: This study demonstrates a clinical remission rate of 53% for patients with mild to moderate ulcerative colitis who were treated with AZA. One year follow-ups showed that continuous suspension of steroid treatment had been achieved in 53% of patients. AZA is an inexpensive and safe therapeutic option which can be considered prior to initiating biological therapy for these patients.