In this study, 60 gastrointestinal stromal tumors of the stomach were analyzed to elucidate the possible relation of their morphology to the mutation status of KIT and PDGFRA genes. The patients included 27 men and 33 women with a mean age of 63.8 years (range, 12-92 years). Only 1 tumor occurred before the age of 21 years. KIT mutations were detected in 31 cases (51.7%), PDGFRA mutations in 22 cases (36.7%), and 7 cases (11.7%) were KIT and PDGFRA wild type. When the mutation status was correlated with histologic features of the tumors, epithelioid or mixed epithelioid/spindle cell pattern and mast cell infiltration were found as the most reliable signs of PDGFRA mutation. Neoplastic rhabdoid cells and multinucleated giant cells, also previously reported as features of PDGFRA-mutated gastrointestinal stromal tumors, seemed to be less specific but still helpful markers in our study. Finally, tumor-infiltrating lymphocytes and myxoid stroma do not seem to be valuable histologic signs.