A 4-month-old male infant was brought to the emergency department because of striking petechial skin lesions and acrocyanosis. Routine hematology revealed leukocytosis and thrombocytosis and the infant was admitted for further investigations. Laboratory findings showed no evidence of infection, and a bone marrow aspirate demonstrated a normal number of immature cells of all lineages. Coagulation and routine biochemistry analyses were within the normal range. Three months later, the infant developed signs and symptoms of encephalopathy with episodes of hypotonia and an altered state of consciousness. A brain magnetic resonance imaging suggested the possibility of an inborn error of metabolism. The urinary organic acid and acylcarnitine profile indicated ethylmalonic encephalopathy. Mutation analysis of the ethylmalonic encephalopathy 1 (ETHE1) gene confirmed the diagnosis of ethylmalonic encephalopathy at the molecular level.