Background: Telotristat ethyl is a tryptophan hydroxylase inhibitor in development for the treatment of carcinoid syndrome (CS) in patients who receive somatostatin analog (SSA) therapy. In TELESTAR, a pivotal Phase 3 study, telotristat ethyl significantly reduced bowel movement (BM) frequency compared to placebo. Objective: The objective of this study was to psychometrically assess meaningful change in BM frequency using data collected within the TELESTAR study. Methods: An anchor-based approach consisted of mapping change from baseline in BM frequency to other patient reported assessments of change. These included the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire - Core Questionnaire (EORTC QLQ-C30) Diarrhea Symptom responders, the EORTC GI.NET21 GI Symptom responders, and patient reported adequate relief at Week 12 (responders had a ≥ 10-point decrease in scores from Day 1 to Week 12). Parameters included within group mean change from baseline to Week 12, t-tests of the change (Wilcoxon Rank Sum for adequate relief), effect size (ES: calculated as the difference between mean on-treatment and baseline BM frequency, divided by the standard deviation of the baseline), and related confidence intervals. Results: There were 135 patients with CS, with a mean age of 63.6 years and mean baseline BM frequency of 5.7 BM/day. Anchor-based analyses indicated significant differences in BM frequency between adequate relief groups at Week 12 (ES: -1.58 vs. -0.79; p = 0.014), responders and non-responders on the EORTC QLQ-C30 Diarrhea Symptoms domain (ES: -1.24 vs. -0.59; p < 0.0001), and responders and non-responders on the EORTC GI.NET21 GI Symptoms Domain (ES: -1.49 vs. -0.75; p = 0.0053). These corresponded to BM frequency reductions of 1.7-1.9 BM/day, or ≥ 30%. Conclusions: Results of this study indicated that patients with CS experienced clinically meaningful reductions in BM frequency of ≥ 30% over the course of 12 weeks.