Biotinidase deficiency is an inherited disorder which has autosomal recessive pattern; it occurs in approximately 1 in 60,000 live births. Usually it manifests seborrheic dermatitis, alopecia, ataxia, convulsions, hypotonia, developmental delay, hearing loss, chronic lactic acidosis and immune deficiency. Its diagnosis is made by the measurement of serum biotinidase enzyme activity and determination of the enzyme. Herein presented that a two and half-month-old boy with biotinidase enzyme deficiency which had cerebral atrophy without any skin signs. In the patients presented with refractory convulsions with unexplainable etiology without any skin lesions, as in our patient, biotinidase enzyme deficiency should be considered and the treatment should be established in early period to prevent many complications that may develop.