Biotinidase deficiency is an inherited metabolic disorder with a very good prognosis if diagnosed and treated early. Cost-effectiveness has been demonstrated. therefore biotinidase deficiency is covered by newborn screening in many countries around the world. In countries like Turkey, where consanguineous marriages are common, morbidity and mortality have been prevented in a large number of individuals with early treatment through national screening programs. The prevalence of biotinidase deficiency varies from country to country and from region to region. Since false positivity and negativity may occur, the diagnosis should be confirmed by quantitative method and molecular genetic analysis.