Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia (AML). All-trans retinoic acid (ATRA) is the first-choice therapy for the treatment of this disease, but has been associated with side effects, the most serious of which is retinoic acid syndrome (RAS). RAS is characterized by unexplained fever, dyspnea, pulmonary infiltrate, leukocytosis and nephropathy. Genital ulcers have been described in some cases, but only two cases of oral ulcers related to this syndrome have been described in the literature. This paper describes the third case of oral ulceration related to ATRA in a 32-year-old white man with diagnosis of APL. Clinicians should know the side effects of ATRA and identify oral ulcers resulting from this therapy. The prompt identification of these ulcers enables the institution of appropriate treatment and can therefore contribute to continuation of the patient's cancer treatment.