Unilateral proptosis is a rare initial presenting sign of acute myeloid leukemia (AML). We report a case of unilateral proptosis in a six-year-old girl as the initial manifestation of AML. The cancer link was initially missed and the case was investigated as one of hyperthyroidism. Peripheral blood smear and bone marrow aspirate evaluation showed signs diagnostic of AML. Computed tomography scan of orbits showed infiltrative process in the right orbit, right maxillary, and right ethmoidal sinuses. Unilateral proptosis as an extramedullary first presenting feature of AML is very rare; however, it should always be considered in the differential diagnosis of proptosis in pediatric age group.