Recurrent somatic mutations in MED12 exon 2 have recently been reported in uterine leiomyomas. The recurrent nature of the mutations strongly suggests that the mutations may play important roles in the pathogenesis of uterine leiomyomas. The aim of our study was to see whether MED12 exon 2 mutations occur in other human tumors besides uterine leiomyomas. We also attempted to confirm occurrence of the MED12 mutations in uterine leiomyomas of Korean patients. For this, we analyzed 1,862 tumor tissues, including a variety of carcinomas, leukemias and stromal tumors by single-strand conformation polymorphism analysis. We found MED12 mutations in 35 uterine leiomyomas (35/67; 52.2%) and one colon carcinoma (0.3%), but none in other tumors. The MED12 mutations consisted of missense (77%) and inframe insertion-deletion (23%) mutations, the pattern of which was similar to the earlier report. Our data indicate that MED12 exon 2 mutations may be tissue-specific to uterine leiomyoma and rare in other tumors. Our study suggests that the MED12 mutations play unique roles in the pathogenesis of uterine leiomyomas and mutated MED12 could be therapeutically targeted in uterine leiomyomas.