Three children with acute lymphoblastic leukemia (ALL) developed isolated optic nerve relapse as the initial site of disease recurrence. They were part of an early cohort of 39 children with non-B-cell, non-T-cell ALL without central nervous system (CNS) involvement, treated regardless of initial leukocyte count with intrathecal chemotherapy for CNS prophylaxis. Although the optic nerve is a known site of relapse in patients with systemic and meningeal ALL, it has not been reported to occur in otherwise relapse-free patients. Early diagnosis and treatment prevented blindness and allowed for long-term survival (57+, 49+, and 97+ months, respectively) and possibly cure. Since these patients were treated in a new manner and exhibited a new pattern of relapse, their clinical courses were reviewed. Features considered worrisome, but not diagnostic of CNS leukemia may be of greater import when intrathecal medications are utilized as primary CNS prophylaxis. An expanded definition of CNS leukemia may be necessary.