Systematic sequence profiling of the Glioblastoma Multiforme (GBM) genome has recently led to the identification of somatic mutations in the isocitrate dehydrogenase 1 (IDH1) gene. Interestingly, only the evolutionarily conserved residue R132 located in the substrate binding site of IDH1 was found mutated in GBM. At present, the occurrence and the relevance of p.R132 (IDH1^R132) variants in tumors other than GBMs is largely unknown. We searched for mutations at position R132 of the IDH1 gene in a panel of 672 tumor samples. These included high‐grade glioma, gastrointestinal stromal tumors (GIST), melanoma, bladder, breast, colorectal, lung, ovarian, pancreas, prostate, and thyroid carcinoma specimens. In addition, we assessed a panel of 84 cell lines from different tumor lineages. Somatic mutations affecting the IDH1^R132 residue were detected in 20% (23 of 113) high‐grade glioma samples. In addition to the previously reported p.R132H and p.R132S alleles, we identified three novel somatic mutations (p.R132C, p.R132G, and p.R132L) affecting residue IDH1^R132 in GBM. Strikingly, no IDH1 mutations were detected in the other tumor types. These data indicate that cancer mutations affecting IDH1^R132 are tissue‐specific, and suggest that it plays a unique role in the development of high‐grade gliomas. Hum Mutat 30, 7–11, 2009. © 2008 Wiley‐Liss, Inc.