OBJECTIVE Gastrointestinal stromal tumors (GIST) are mesenchymal tumors originating from the gastrointestinal canal wall. Although a number of studies are performed concerning prognostic factors, no indicators of recurrence or metastasis could be established. In this study we assessed the prognostic value of MIB-1 proliferative index (PI) in GIST, and whether there was a relationship to any other clinicopathological findings. METHODS In the study 37 patients with GIST diagnosis were included. The cases were classified as low, intermediate, and high risk groups according to tumor size and mitotic activity. The average PI of 10% in high risk group was set as the cut-off value. RESULTS Of all the cases, those with a MIB-1 PI over the cut-off value had a significantly shorter survival (Log-rank test, p < 0.05). Likewise cases with small bowel tumors with a MIB-1 PI over the cut-off value had a significantly shorter survival (Log-rank test, p < 0.05). A statistically significant negative correlation was found between presence of necrosis and survival using McPearson correlation test (p < 0.01). CONCLUSIONS MIB-1 PI and presence of necrosis are possible indicators of prognosis especially in GIST cases of the small bowel.