Background: NAT genes are considered candidate genes for the genetic predisposition to non-syndromic Cleft lip with or without cleft palate (NSCLP), since they codify for N-acetyltransferases, enzymes responsible for the biotransformation of arylamines, hydrazine drugs, and a great number of toxins and carcinogens present in diet, cigarette smoke, and environment., Aim: To determine the association between alleles determining slow acetylator phenotype and the risk of NSCLP., Material and Methods: We analyzed *5 (481C>T), *6 (590G>A) and *7 (857G>A) alleles which determine the slow acetylator phenotype and *4 (wild type) allele by polymerase chain reaction/restriction fragment length polymorphism in 97 progenitor-case trios of NSCLP in Argentinian Obstetric Wards. We evaluated the transmission disequilibrium (TDT)., Results: TDT showed a positive association between allele *5 and NSCLP (odds ratio = 1,6; p = 0,03)., Conclusions: The presence of *5 allele is significantly higher in cases with congenital NSCLP.