Phenylketonuria(PKU) is an inborn error of metabolism, inherited in an autosomal recessive fashion resulting in >98% of cases from phenylalanine-hydroxylase(PAH) gene defect that leads to mental retardation if not treated. Early diagnosis of PKU is possible due to neonatal screening, initiated in 1989 in the Republic of Moldova. Patient genotyping for PAH gene mutations has been used in predicting the evolution and individualization of disease treatment based on evidence from the BIOPKU database (http://www.biopku.org) and literature. 127 patients with PKU are registered in the Republic of Moldova. The analysis of pathogenic mutations was performed by PCR/RFLP methods and Sanger sequencing of the PAH gene. In 6 cases the DNA samples were damaged. The 121 patients, 45 genotypes were identified. Only 30 genotypes were reported in the BIOPKU database, 11 genotypes were found in the literature and 4 genotypes were not included in any of the sources. In 73.33% they corresponded to the classic PKU forms, requiring the hypophenylalanine diet as the treatment of choice, and 26.67% - Hyperphenylalaninemia. Responsiveness to BH4 was assessed based on evidence from the databases used. Thus, 5.10% of the total group were considered probably responsive at BH4, and 13.26% - responsive. This study allows to conclude that about 20% of patients with PKU in the Republic of Moldova can be tested with BH4, with a potentially positive result, thus improving treatment with BH4 therapy. In addition, the BIOPKU database could be supplemented with the cases of 4 patients whose genotypes have not yet been registered