INTRODUCTION: Infant vitamin B deficiency can manifest as a severe neurodegenerative disorder and is usually caused by maternal deficiency due to vegetarian diet or pernicious anaemia. Its early recognition and treatment can prevent potentially serious and irreversible neurologic damage. Biochemically, vitamin B deficiency leads to an accumulation of methylmalonic acid, homocysteine, and propionylcarnitine. Expanded newborn screening using tandem mass spectrometry may identify neonatal and maternal vitamin B deficiency by measurement of propionylcarnitine and other metabolites in the dried blood spot sample of newborns. AIM: To summarize our experiences gained by screening for vitamin B deficiency. METHOD: Clinical and laboratory data of vitamin B-deficient infants diagnosed in Szeged Screening Centre were retrospectively analysed. RESULTS: In Hungary, expanded newborn screening was introduced in 2007. Since then approximately 395 000 newborns were screened in our centre and among them, we identified four newborns with vitamin B deficiency based on their screening results. In three cases an elevated propionylcarnitine level and in the fourth one a low methionine level were indicative of vitamin B deficiency. We also detected an additional vitamin B-deficient infant with neurological symptoms at 4 months of age, after a normal newborn screening, because of elevated urinary methylmalonic acid concentration. Vitamin B deficiency was secondary to maternal autoimmune pernicious anaemia in all the five infants. As a result of the recognized cases the incidence of infant vitamin B deficiency in the East-Hungarian region was 1.26/100 000 births, but the real frequency may be higher. Conslusions: Optimizing the cut off values of current screening parameters and measuring of methylmalonic acid and/or homocysteine in the dried blood spot, as a second tier test, can improve recognition rate of vitamin B deficiency. Orv Hetil. 2017; 158(48): 1909-1918.