Background: Prediction of biological behavior is crucial for selection of new therapeutic modalities in GIST. Here, we aimed to assess whether KIT and PDGFRA mutations have survival impact in gastrointestinal stromal tumors (GIST). Patients and Methods: Fifty-five Brazilian patients with completely resected GIST were examined for KIT and PDGFRA mutations. The 5-year disease-free survival (DFS) was analyzed. Results: KIT and PDGFRA mutations were identified in 74.5% and 7.3% of patients, respectively. The 5-year DFS rate for all patients was 52.8%. The 5-year DFS rate was lower in patients with tumors having inframe deletions or concomitant in-frame deletions and insertions affecting codons 557-558 than in patients with tumors having other exon 11 KIT mutations (p=0.023). Conversely, when the patients with concomitant deletioninsertion mutations affecting codons 557-558 were excluded from the analysis, deletions involving codons 557-558 had no influence on 5-year DFS rates. Conclusion: Our findings indicate that a specific KIT mutation may be associated with unfavorable behavior in GIST. This finding may have implications on selecting patients for adjuvant therapy.