One of the most common genetic events in acute myeloid leukemia (AML) is the t(8;21) (q22;q22) translocation, which contributes to leukemic transformation. However, different lines of evidence suggest that the AML1-ETO rearrangement is not sufficient to cause the full leukemic phenotype. Secondary genetic alterations such as mutations in receptor tyrosine kinases are thus required to induce overt AML. The incidence of c-KIT mutations in exon 17 was evaluated in 37 Spanish patients with AML1-ETO+ leukemias. c-KIT mutations were present in only two cases (6.6%) and were shown to be associated with an adverse outcome. The frequency of c-KIT mutations described here is much lower than in other reports.