Abstract Background Ulcerative colitis (UC) therapy management is complex and typically begins with conventional therapy (CVT) followed by biologic drugs. For many years, CVTs were the only available option for the treatment of UC in the public healthcare system in Brazil (SUS). Biologic therapy was only available at the end of 2020. This study aimed to observe the real-world intestinal complications (IC) experienced in patients with UC receiving CVT in SUS. Methods This study was a secondary analysis of patients (>18 years) with UC (ICD-10 code: K51) who received at least two claims of CVT (index data defined as first CVT), between January 2011 and February 2020, in the DATASUS database. UC IC was defined as at least one claim (after index date) for either: UC-related hospitalisation, pre-defined procedure codes for rectum or intestinal surgeries, pre-defined ICD-10 codes were validated by independent clinical experts (malignant neoplasia of colon, stenosis, haemorrhage, ulcer and other rectum and anus disease, megacolon, functional diarrhea volvulus, intussusception and erythema nodosum). Patients with an anal or rectal fissure or fistula, with <6 months of follow-up from index date, with a CVT claim 12 months before index date or patients treated outside of the public healthcare system, were excluded. Descriptive statistics, annual incidence and incidence rate (IR; per 100 patient-years [PY]) over the available follow-up period were calculated. Results In total, 41,229 patients with UC were included (median age, 48 years; 65% women) and the median (interquartile range [IQR]) follow-up period was 3.3 (1.8 - 5.3) years. CVT utilized during follow-up was: mesalazine (87%), sulfasalazine (15%), azathioprine (16%) or methotrexate (1%); the median (IQR) CVT duration was 1.9 (0.8 – 4.0) years. The overall IR of IC was 2.5 per 100 PY during the follow-up period. Of the IC, 54% were related to ICD-10, 20% were related to a procedure and 26% to a UC-related hospitalisation (Table 1). The overall annual incidence of IC was 2.9%, 2.6% and 2.5% in the first, second and third year after index, respectively (Table 2). Over the first 3 years, the annual IR of UC-related hospitalisations ranged from 0.8% to 1.1%, for ICD-10 related events 0.9%-1.2% (anus and rectum disease, and malignant neoplasia of colon most frequently reported) and for procedure-related events 0.6%-0.7% (intestinal resection and polyp removal were the most frequent procedures). Conclusion The IR of IC was constant along the use of CVT. This study suggests the need to consider additional strategies for intestinal complications associated with the management of UC in Brazil, including but not limited to biologics.