I report on a 21-year-old man with acute promyelocytic leukemia (APL) which relapsed after a therapeutic regimen consisting of tretinoin, daunorubicin, enocitabine, mitoxantrone, and cytarabine. The patient also had severe mental retardation caused by a congenital central nervous system malformation. Administration of arsenic trioxide (As₂O₃) is indicated for patients with APL, however, daily intravenous infusion of As₂O₃ presented problems because of the patient's violent resistance to venous access. Accordingly, 10mg of an oral solution of As₂O₃ was given once daily for 70 days. No adverse events were observed with the exception of transient hyperleukocytosis and fever. The patient achieved molecular remission 103 days after the start of oral As₂O₃, and remains in remission after an additional 2 courses of oral As₂O₃ as consolidation chemotherapy. Oral As₂O₃ may be useful in the treatment of relapsed APL as an alternative to intravenous As₂O₃.