Traditional cytogenetic methods have relied on tissue culture techniques to generate adequate mitotic cells for the analysis of chromosome disorders for prenatal diagnosis. Chromosome banding techniques allow the evaluation of mitotic cells for structural and numerical aberrations and define the nature of any rearrangement. With the advent of fluorescent in situ hybridization methodology, which combines the molecular technologies of chromosome-specific probes and in situ molecular hybridization, it has become possible to analyze chromosomal numerical and structural aberrations from interphase cells. The use of molecular cytogenetic techniques should greatly increase the speed and diagnostic resolution of clinical specimens.