Pearson disease is a rare, usually fatal, mitochondrial disorder affecting primarily the bone marrow and the exocrine pancreas. We report a previously healthy 10-week-old girl who presented with profound macrocytic anemia followed by pancytopenia, synthetic liver dysfunction with liver steatosis, and metabolic acidosis with high lactate levels. She had no pancreatic involvement. Multiple cytoplasmic vacuoles in myelocytes and monocytes were seen upon microscopic evaluation of the bone marrow. Genetic analysis of the mitochondrial genome revealed a 5 kbp deletion, thus establishing the diagnosis of Pearson disease.