Stromal tumors of the abdominal colon, the least common of all gastrointestinal stromal tumors, have not been well characterized. They have often been lumped with stromal tumors of the anorectum in order to achieve significant numbers for analysis, yet there are no data to prove that stromal tumors from these two sites are the same. In this study, we evaluated 20 colonic stromal tumors to identify clinical, morphologic, and immunophenotypic features that were useful in discriminating between those that had metastasized or caused death from those that had not metastasized or caused death. We found that colonic stromal tumors are morphologically heterogeneous, and the malignant ones are clinically aggressive. They often have metastases at presentation, and cause death in a short time. An infiltrative growth pattern in the muscularis propria, invasion of the mucosa, and high mitotic counts correlated significantly both with metastases and with death from tumor. We also found that dense cellularity correlated significantly with metastases, but not with death, and that coagulative necrosis correlated with death, but not with metastases.