Leukemic patients with extremely high white blood counts may exhibit the phenomenon of leukocyte larceny, in which white blood cells metabolize plasma oxygen in arterial blood gas samples (ABG) producing a spuriously low oxygen tension. We report the case of a leukemic patient with a white blood count in excess of 500,000 in whom multiple ABGs documented hypoxemia out of proportion to his clinical picture. Pulse oximetry was used to confirm higher hemoglobin oxygen saturation to establish the leukocyte larceny.