Five species belonging to the genusGampsocleisFieber, 1852 were analyzed using fluorescencein situhybridization (FISH) with 18S rDNA and telomeric probes, as well as C-banding, DAPI/CMA₃staining and silver impregnation. The studied species showed two distinct karyotypes, with 2n = 31 (male) and 2n = 23 (male) chromosomes. The drastic reduction in chromosome number observed in the latter case suggests multiple translocations and fusions as the main responsible that occurred during chromosome evolution. Two groups of rDNA distribution were found inGampsocleisrepresentatives analyzed. Group 1, with a single large rDNA cluster on the medium-sized autosome found in four species, carried in the haploid karyotype. Group 2, represented only byG.abbreviata, was characterized by the presence of two rDNA signals. TTAGG telomeric repeats were found at the ends of chromosome arms as expected. The rDNA clusters coincided with active NORs and GC-rich segments.