In the few published karyotypes of human medulloblastoma, multiple chromosome abnormalities have usually been demonstrated. We report a case of medulloblastoma in which only a single structural alteration was observed, namely an unbalanced translocation between chromosomes 1 and 6 resulting in partial 1q trisomy and partial 6q mónosomy. This finding may help define genomic regions that are of importance in development of medulloblastoma.