The major aneuploidies diagnosed prenatally involve the autosomes 13, 18, 21, and sex chromosomes X and Y. Fluorescence in situ hybridization (FISH) allows rapid analysis of chromosome copy number in interphase cells. We retrospectively reviewed 130 amniotic fluid interphase FISH analyses from January 1997 to December 2001. The review was done in order to assess the role of interphase FISH among the patients who were at the risk of fetal aneuploidies. The sample was considered to be aneuploid when 70% of or more than the total number of hybridized nuclei displayed the same abnormal hybridization pattern for a specific probe. All of 130 cases but one met the criteria. The results were considered as informative and they were obtained in 24-48 hr. The overall detection rate for aneuploidies was 100% (2 cases of trisomy 21, 2 cases of trisomy 18, and 1 case of Turner syndrome). In comparison to cytogenetics, the rates of both sensitivity and specificity were 100%. The experiment demonstrates that FISH can provide a rapid and accurate clinical method for prenatal identification of chromosome aneuploidies. The experiment can also serve as an adjunctive test to help cytogenetics to reduce significant amount of emotional stress of patients and physicians through early decision making process.