To describe the clinical presentation and imaging features of a patient with optic nerve leukemic infiltration as the first site of relapse after complete response to systemic treatment. We report the case of a 23yr old man with history of Acute Lymphoblastic Leukemia (ALL) in complete remission. Six months later, the ocular examination revealed decreased visual acuity. Fundus examination showed a pale optic disk with blurred margins and multiple flame-shaped and dot and blot retinal hemorrhages in his left eye. A diagnosis of leukemic infiltration to the optic nerve was made by Magnetic Resonance Imaging (MRI). Cytological analysis of the cerebrospinal fluid did not show any abnormal cells or blasts. A course of oral corticosteroid therapy was prescribed and 20Gy of radiation was administered to the whole brain including the left orbit. Vision was improved dramatically in the left Eye. Isolated optic nerve relapse of leukemic infiltration is of paramount importance to early diagnosis, as vision can be saved if treatment with orbital radiotherapy if initiated promptly.