Analysis of a pediatric germ cell tumor by conventional cytogenetic investigation and fluorescence in situ hybridization showed consistently the presence of two isochromosomes 12p, loss of the maternal band 1p36, and other numerical and structural chromosome changes. The rearrangements observed resulted mainly from breaks occurring at paracentromeric regions. This report represents the first description of i(12)(p10) in a pediatric testicular embryonal carcinoma.