To evaluate the clinical effectiveness of preimplantation genetic diagnosis (PGD) for the couples having a higher risk of genetic diseases with fluorescence in situ hybridization (FISH).Ovarian hyperstimulation, oocyte retrieval and in vitro fertilization were performed in 4 cases. Blastomere biopsy were performed from the embryos at the 6 - 8 cell stage. Genetic diagnosis was identified by single blastomere FISH. The female embryos or normal embryos were transferred into uterus.Twelve embryos were available for embryo biopsy. Twenty cells were collected. Seventeen nuclei were found after fixation. Hybridization signals of 11 embryos were clear and 8 embryos were transferred into uterus. One clinical pregnancy was achieved, and 1 normal female infant was delivered on september 14, 2001.PGD is very valuable for avoiding selective abortion and birth of affected child of the couples having a higher risk of genetic diseases by detecting embryo sex and chromosome number using FISH.