The fluorescence in situ hybridization method allows the observation of chromosomal aberrations under a microscope at the cellular level. However, the extent to which the FISH method reflects actual chromosomal aberrations is unknown. To estimate the accuracy of detecting aberrations by FISH, we performed dual color-FISH with two different DNA probes for the principal target DNA and assessed their concordance. The two DNA probes used were a whole chromosome painting probe and an alpha satellite probe. A high concordance rate of 82%-98% was found between the probes, indicating that the accuracy of determining chromosomal aberrations by FISH is high.