Two infants with early presentation of biotinidase deficiency (age 3 weeks and 2 weeks) are described. On admission, both children had severe neurological symptoms. In the first patient, magnetic resonance imaging (MRI) of the brain showed frontal and temporal atrophy, and in the second patient, CT of the brain showed diffuse periventricular hypodensities, particularly in the frontal region. Oral treatment with biotin (15mg and 10mg per day respectively) made all symptoms disappear within a few weeks. On follow-up 13 and 16 months later, both children were still asymptomatic on this treatment. Their psychomotor development was normal. MRI and CT of the brain had normalized. Later, a moderate hearing loss was detected in the first patient. In biotinidase deficiency, early diagnosis and treatment with oral biotin are essential in order to prevent irreversible damage to the central nervous system and early death from metabolic acidosis. Neonatal screening for biotinidase deficiency would fulfil this goal.