Ophthalmic and neurologic involvement in chronic lymphocytic leukemia is uncommon, and if it does occur, it is usually only late in the course of the disease. We report three cases in which progressive visual loss from optic nerve infiltration was an early clinical manifestation of chronic lymphocytic leukemia. Progressive optic atrophy with loss of acuity and visual field occurred in all cases, preceded in one patient by transient visual obscurations and disc edema. Surface marker studies of cerebrospinal fluid lymphocytes were useful in differentiating leukemic optic nerve infiltration from other causes of optic nerve damage. Optic nerve irradiation gave considerable clinical improvement in all three cases.