Point mutations affecting codons 12, 13 (exon 1) and 61 (exon 2) of the N-RAS gene and codons 12 and 13 (exon 1) of the K-RAS gene are identified in approximately 30.0% and 10.0%, respectively, of multiple myeloma (MM) patients living in the northern hemisphere. To date, there are no reports about the prevalence of RAS gene mutations in MM Brazilian patients, and this comprised the aim of the present study. DNA from bone marrow aspirates of 252 patients with MM (139 males and 113 females; aged 59.33 +/- 11.95 years) were investigated for whole exons 1 and 2 of the N-RAS gene and whole exon 1 of the K-RAS gene by direct sequencing of DNA amplified in vitro by the polymerase chain reaction. Fifty-three out of 252 (21.03%) MM patients presented RAS mutations. Heterozygous mutations at codons 4, 10 (exon 1), 61 and 65 (exon 2) of the N-RAS gene were identified in seven out of 252 (2.78%) patients. K-RAS heterozygous mutations at codons 7, 12, 13 (exon 1) were seen in 46 out of 252 (18.25%) patients. To the best of our knowledge, the mutation at codon 7 of K-RAS gene is reported for the first time in MM. Taken together, these results suggest that Brazilian MM patients are characterized by: (i) a low prevalence of RAS mutation and (ii) RAS mutations located at distinct regions of the critical codons of the N-RAS and K-RAS genes.