We describe a patient with an acute promyelocytic leukemia (APL) previously treated with two courses of cytarabin, idarubicin and all-trans retinoic acid (ATRA), who presented a medullary and meningeal relapse after 8 months of complete remission. A diagnosis of central nervous system (CNS) involvement was based on the appearance of APL blasts in the cerebrospinal fluid (CSF); magnetic resonance (MR) imaging was negative. The neurological symptoms were not evident at the time of recognition of the medullary recurrence, but appeared a few days later, when the patient had already received a reinduction treatment. When the CSF was first examined, showing atypical promyelocytes, there was no excess of blasts on bone-marrow examination. The patient was treated with ATRA and intrathecal administrations of cytoxic drugs, achieving a complete long-lasting CNS remission. The appearance of mature myeloid cells in the CSF during this treatment suggested a possible differentiating effect of ATRA towards extramedullary relapse.