Abstracts instability on 22 patients using variable types and concentrations of these alkylating (25 and 40 ng/ml of MMC, 0.1µg/ml of DEB). Methods Heparanized venous blood samples were collected and were processed for the cytogenetic methodology in this study. After culture, 100 of metaphases were analysed to evaluate the frequency of chromosomal aberrations. Results The MMC test at 25ng/ml was High sensitive for FA. The DEB test showed a better specificity. The study of the mitotic segregation of sexual chromosomes by FISH took away any abnormality of the segregation to cells FA. Conclusions A molecular study of the sensivity and the specificity of the alkylating agents used according to the group of complementation will come refine the diagnosis of FA by establishing a gold standard. CLINICAL AND CYTOGENETIC STUDY IN 116 CHILDREN COHORT WITH SEXUAL AMBIGUITY