Tumor necrosis is associated with poor clinical outcomes in many malignancies. We aimed to determine whether tumor necrosis was an independent predictor of outcomes in gastric gastrointestinal stromal tumors (GISTs). We retrospectively analyzed data from 740 patients undergoing curative resection for gastric GIST at four centers between 2001 and 2015. Disease-free survival (DFS) was estimated with the Kaplan-Meier method, and associations with prognosis were assessed with Cox regression models. Tumor necrosis was present in 122 cases (16.5%). The prevalence of tumor necrosis increased with higher risk-stratification, including 0.7%, 7.4%, 17.3%, and 39.3% for very low-, low-, intermediate- and high-risk tumors, respectively (P<0.001). Tumor necrosis was associated with aggressive tumor biology, such as larger tumor size, higher mitotic index, tumor rupture, and presence of nuclear atypia (all P<0.05). Multivariate analysis revealed that tumor necrosis was an independent predictor of unfavorable DFS (HR: 2.641; 95% CI: 1.359-5.131; P=0.004). When stratified by the modified National Institutes of Health (NIH) classification, tumor necrosis still independently predicted DFS in high-risk patients (P=0.001) but not in non-high-risk patients (P=0.349). The 5-year DFS rate in high-risk patients with and without tumor necrosis was 56.5% and 82.9%, respectively (P=0.004). Notably, the prognostic significance of tumor necrosis was maintained when the patients were stratified by age, sex, tumor location, tumor size, and mitotic index (All P<0.05). Tumor necrosis is a useful predictor of outcomes in gastric GIST, especially in high-risk patients. Based on these results, we recommend that the current NIH classification should be further improved and expanded to include tumor necrosis as a valuable prognostic indicator.