Glioblastoma is the most common primary tumor of the central nervous system, but the underlying genetic changes that give rise to these tumors are still poorly understood. We report a primary glioblastoma with an unusual age of presentation. The patient was a 22-year-old man with a survival of 16 months. Morphological findings showed an increase of cellularity with positive GFAP and EGFR expression, increase of proliferate index, vascular hyperplasia with glomeruloid structures and necrosis. Molecular analysis showed EGFR amplification. No mutations of the TP53 or amplification of MDM2 and CDK4 were detected. Neither homozygous deletion of the 9p21 locus genes nor aberrant methylation were found. The cytogenetic study showed a clonal karyotype. The metaphases presented, among other anomalies, a small ring chromosome and double-minutes chromosomes. Using FISH and CGH techniques, it was found that the ring chromosome was a partial trisomy of chromosome 7, and the region implicated corresponded to 7p13-q21. Partial trisomies in glioblastoma could play an important role in defining those regions where genes implicated in this tumor process may be found. We studied the possible correlation of these findings with the tumoral phenotype.