RAS genes are the most frequently mutated oncogenes detected in human cancer. In this study we analyzed the presence of mutations at codon 12 of the KRAS gene in 78 women with ovarian tumor, including 64 invasive ovarian cancers and 14 borderline ovarian tumors, using an RFLP-PCR technique and we evaluated whether such alterations were associated with the selected clinicopathological parameters of the patients. KRAS codon 12 gene mutations were found in 6,2% of ovarian cancer tissue and in 14,3% of the borderline ovarian tumor. KRAS mutations were found with a significantly higher frequency in mucinous and borderline tumors compared to serous tumors (p<0,01). Mutation frequency was correlated with the histological type of tumor, but not with stage, grade or patients age.