Knowledge on the genetic diversity of wild fish species is essential for conservation and appropriate management of individuals in repopulation programs. In Colombia, Brycon henni has been reported in the Magdalena and Cauca river basins, but the population and range have diminished as a consequence of anthropic activities. In this study, the Random Amplified Polymorphic DNA (RAPD) was used to estimate the actual genetic structure in this species. For the purpose, six sample sites located in the department of Antioquia (Central Chain Mountains of Colombia) were used. Thirty five primers (87.5%), out of forty used, yielded 1 466 reliable and consistent fragments; 417 were considered as unique fragments able to discriminate among the Magdalena (Humarada-1 and Humarada-2) and Cauca (Piedras, La Clara y Guaracfi) river basins samples, suggesting that each is a discrete unit. This diversity suggests that anthropic effects of over fishing, dam building, deforestation and water pollution, have contributed to the isolation of these fish groups on the high mountains. Brycon moorei and Colossoma macropomum, as an interspecific control groups, were placed out of the B. henni general group, confirming their taxonomic classification through morphologic data. The RAPD technique was useful to know the genetic diversity and to discriminate among B. henni populations from different geographic origins, as a basis for an appropriate plan of repopulation, conservation and wildlife management.