Background: The Ulcerative Colitis Patient-Reported Outcomes Signs and Symptoms (UCPRO/SS) measure was recently developed to evaluate symptom outcomes in clinical trials of ulcerative colitis (UC). Aim: To examine the structure, reliability and validity of the UCPRO/SS. Methods: An observational study was conducted in adults with UC and included three clinic visits: Day 1 (Visit 1), Day 7 (Visit 2), and Day 28 (Visit 3). Subjects completed the UC-PRO/SS on a daily basis using an electronic device. Descriptive statistics, factor analysis, and Rasch analysis were conducted to determine final structure. Test-retest reliability was assessed among stable subjects, defined as those with no on patient-reported global rating of change in UC severity from Visit 2 to Visit 3, using paired t-test and intraclass correlation coefficients (ICCs). Cronbach's coefficient alpha was used to assess internal consistency. Construct validity was examined based on correlations with the Inflammatory Bowel Disease Questionnaire (IBDQ), Partial Mayo Score, and other ancillary measures. Known-groups validity was evaluated by comparing UC-PRO/SS domain scores by groups defined by the Partial Mayo Score, Patient Global Rating of Disease Severity, and Clinician Global Rating of Disease Severity using ANCOVA models adjusted for age and gender. Results: Of the 200 participants, 117 (59%) were female; mean (SD) age was 46 (14.6) years. The 14-item UC-PRO/SS includes three domains: Bowel Movement (BM) Signs and Symptoms, Abdominal Symptoms, and Systemic Symptoms. Alpha coefficients ranged from 0.66 to 0.80. No significant differences were observed in UC-PRO/SS domain scores between visits for stable subjects, with ICC values of 0.71-0.81. The BM Signs and Symptoms scale was strongly correlated to the Partial Mayo Score (0.79) and moderately to strongly correlated with the IBDQ (0.51 to 0.73). Moderate correlations (0.45-0.65) were observed between Abdominal Symptoms and Partial Mayo Score, IBDQ, and BPI Worst Pain. Similar correlations were observed for Systemic Symptoms. Findings indicate that UC-PRO/SS domain scores were significantly different (p<0.0001) by known groups. Conclusions: Findings from this study support the UC-PRO/SS as a reliable and valid measure for the evaluation of signs and symptoms in UC clinical trials. Future studies conducted within the context of a clinical trial will examine relationships with clinicalmeasures to assess treatment response.