Background and Aims: GI ischemia is a concerning adverse event of portal vein thrombosis (PVT). Minimally invasive techniques, such as visible light spectroscopy (VLS), have greatly improved the ability to diagnose GI ischemia. The aim of this study was to assess the clinical presentation and characteristics of GI ischemia in patients with PVT. Methods: Patients with noncirrhotic, nonmalignant PVT were included in this prospective cohort study. Clinical symptoms of GI ischemia were assessed by a structured questionnaire, VLS, and radiologic evaluation of the mesenteric vasculature. VLS measurements were compared with those in patients with cirrhosis and with a reference population. Results: We included 15 patients with chronic PVT and 1 patient with acute PVT (median age 46.1 years [interquartile range [IQR], 30.9-53.7]; 44% male). Decreased mucosal oxygenation in at least 1 location of the GI tract was found in 12 patients (75%). Compared with the reference population (median 60.0 [IQR, 56.2-61.7]), VLS measurements were mostly decreased in the descending duodenum in patients with PVT (median 55.5 [IQR, 52.3-58.8]; P = .02) and patients with cirrhosis (median 52.0 [IQR, 46.5-54.0], P = .003). Symptoms typical for GI ischemia, such as postprandial pain and exercise-induced pain, were reported in 10 patients (63%) with PVT. In patients with extension of thrombosis into the superior mesenteric vein and splenic vein and/or presence of hypercoagulability, decreased VLS measurements were observed compared with historical control subjects. Conclusions: In patients with chronic PVT, GI ischemia is frequent. VLS enables objective and quantitative determination of GI mucosal ischemia. Onset of abdominal symptoms such as postprandial pain should prompt the physician to re-evaluate extent, cause, and treatment of PVT.