Throughout the world, chromosome alterations are one of the main causes of major malformations in newborns and of multiple clinical characteristics in patients of other ages. The present study had as its principle objective to determine the distribution of chromosome alterations obtained from 1999-2009 at a private laboratory located in Monterrey, Nuevo Leon state, Mexico, and that received samples from other northeastern Mexican states. We studied 1,652 cases of peripheral blood karyotypes. Samples were obtained from patients in whom there was a suspicion of some chromosome alteration based on the clinical history. Of the karyotypes evaluated, 1,250 (76.0%) had normal karyotype, 320 (19.0%) presented chromosome alterations, among which 270 (84%) were numerical, 50 (16%) were structural, and 82 (5.0%) were polymorphisms. Chromosome alteration frequency and type found in the present study is similar to that found in studies conducted in other countries and to that reported in the literature.