Vitamin B12 deficiency presents with many different clinical manifestations. Its deficiency may cause hematological, neurological, gastrointestinal,dermatological and cardiac findings. Vitamin B12 deficiency develops easier in infants of vegetarian mothers and infants those not having an access to foodscontaining enough vitamin B12 in the developing countries. In its long-term deficiency, irritability, apathy, loss of appetite and developmental delay mayoccur in the infant. In this report, we present an infant of vitamin B12 deficiency with a history of hypotonicity and growth retardation. We wanted to draw attention to the rapidly recovering neurological findings of this patient whoresponded quickly to treatment.