Chromosome banding studies of peripheral blood lymphocytes were conducted upon 2,448 Korean patients referred to us for suspected chromosomal abnormalities over a 10-year period (1980-1989). A sample of 30 metaphases was examined per individual for a total of 73,440 metaphases. We detected chromosome disorders in 699 patients (28.6%): 429 (61.4%) had numerical aberrations and the other 270 (38.6%) revealed structural rearrangements. The overall abnormality rate of 28.6% in our study is in agreement with other surveys, although our abnormality rate in several disease groups is significantly different from other studies. Whether the discrepancy is real or whether it is simply the result of sampling variation cannot be explained at present.