A subset of glioblastomas (GBMs) carry gene amplifications on chromosomal segment 4q12. To characterize this amplicon in detail, we analyzed a set of 100 samples consisting of 65 GBMs, 10 WHO grade III astrocytomas, 12 oligodendrogliomas, and 13 glioma cell cultures. We applied multiplex ligation-dependent probe amplification to determine the gene dosage of PDGFRA, KIT, and KDR and the flanking genes USP46, RASL11B, LNX1, CHIC2, SEC3L1, and IGFBP7. The amplicon was highly variable in size and copy number and extended over a region of up to 5 Mb. Amplifications on 4q12 were observed in 15% of GBMs and 23% of GBM cell cultures but not in 22 other gliomas. We analyzed transcription and translation of some genes within this amplicon. Gene amplification generally correlated with high transcript levels but did not necessarily result in increased protein levels. However, we detected frequent expression of proteins encoded by PDGFRA, KIT, and KDR in GBMs and GBM cell cultures independent of the amplification status. Future treatment of GBM patients may include drugs targeting multiple kinases that are encoded by genes on chromosomal segment 4q12.