Background/aims: The aim of this multicenter study was to determine the histopathological features and immunohistochemical profiles of gastrointestinal stromal tumors diagnosed in Turkish patients. Material and Methods: Twenty-eight participating centers registered their gastrointestinal stromal tumor cases on a nationwide database. The diagnosis of gastrointestinal stromal tumor relied upon hematoxylin & eosin features and the results of antibody panel including CD117, CD34, desmin, smooth muscle actin, S-100 protein, and Ki67. The database consisted of parameters including age, gender, location, and all other histopathological and immunohistochemical findings. Statistical analysis was performed using Pearson, Kruskal-Wallis, Mann-Whitney U, and Spearman tests. Results: From all of the gastrointestinal stromal tumors in the database, 1160 cases with a male to female ratio of 1.22 and a mean age of 56.75 years were included in the study. The most common location was the stomach (45.0%), followed by the small intestine, omentum-peritoneum, large intestine, and esophagus (32.0%, 12.6%, 9.3%, 1.1%, respectively). The risk groups were distributed as: 6.1% very low, 21.7% low, 19.3% intermediate, and 53% high-risk cases. Many histopathologic findings were correlated with risk groups. CD117 was positive in 95.3% of gastrointestinal stromal tumors, whereas CD34 was positive in 74.9%, smooth muscle actin in 45.9%, desmin in 9.2%, and S-100 in 19.1.%. Though no significant relation was found between CD117 expression and tumor location, CD34, smooth muscle actin and Ki67 expressions significantly varied in different locations (p=0.001) and risk groups. Conclusions: The results of this multicenter study demonstrated that features other than tumor size and mitosis and immune markers other than CD117 and Ki67 included in the antibody panel seem to be useful as predictive risk factors.