To determine the genotype of a triplet resulted from an IVF procedure, with discordant cystic fibrosis (CF) phenotype. Molecular diagnosis of CF. Affected triplet followed at the CF Clinic Center of Children s Hospital Los Angeles was referred to Molecular Genetics Laboratory at Georgetown University Medical Center for comprehensive DNA analysis of the cystic fibrosis transmembrane regulator (CFTR) gene. Three affected children and the healthy parents with negative family history of CF. Temporal temperature gradient gel electrophoresis and direct DNA sequencing were used to detect and to identify the mutations. The child with classic CF had △ F508 and R553X mutations. Two children with mild CF symptoms had △ F508 and R117C. The father carried two mutations, R553X and R117C. The mother is a carrier for △ F508. Mutational analysis of the CFTR gene should always be recommended to the infertile couples seeking for IVF.The CFTR mutation screening would be essential if the man has congenital bilateral absence of vas deferens (CBAVD) despite the negative family history of CF. Option of complete CFTR gene analysis at a cost of about ＄ 1,500- ＄ 2,000 should be made available if one mutation is found in the male partner with congenital bilateral absence of vas deferens. To determine the genotype of a triplet resulted from an IVF procedure, with discordant cystic fibrosis (CF) phenotype. Molecular diagnosis of CF. Affected triplet followed at the CF Clinic Center of Children’s Hospital Los Angeles was referred to Molecular Genetics Laboratory at Georgetown University Medical Center for comprehensive DNA analysis of the cystic fibrosis transmembrane regulator (CFTR) gene. Three affected children and the healthy parents with negative family history of CF. Temporal temperature gradient gel electrophoresis and direct DNA sequencing were used to detect and to identify the mutations The child with classic CF had △ F508 and R553X mutations. Two children with mild CF symptoms had △ F508 and R117C. The father carried two mutations, R553X and R117C. The mother is a carrier for △ F508. Mutational analysis of the CFTR gene should always be recommended to the infertile couples seeking for IVF.The CFTR mutation screening would be essential if the man has c ongenital bilateral absence of vas deferens (CBAVD) despite the negative family history of CF. Option of complete CFTR gene analysis at a cost of about $ 1,500- $ 2,000 should be made available if one mutation is found in the male partner with congenital bilateral absence of vas deferens.