In Hungary the national newborn screening programme for the detection of biotinidase deficiency was launched in 1989. In this study, we determined the genotypes of all patients identified at the Budapest Screening Centre that covers half of the country. The incidence of the disorder in Western Hungary is about three times the worldwide incidence. Overall, 21 different mutations were identified in 49 patients, including four novel mutations. Ten mutations proved to be unique to the Hungarian population.