We report the case of a patient who was admitted to the immunology unit of our medical facility. The patient had a history of recurrent oral ulcers, low-grade fever, weight loss, and fatigue. Echocardiographic examination revealed a right ventricular mass that was initially thought to be a myxoma in an unusual location, and the patient was sent to surgery. Surgery revealed the mass to be a thrombus. After 5 months of anticoagulation therapy, the patient was readmitted to our institution with the same complaints, and a right atrial thrombus was found on echocardiographic examination. After a careful reevaluation of the patient's history and episodes of recurrent oral and genital ulcers, as well as the papulopustular lesions found on his first admission to hospital, Behçet's disease was diagnosed. The patient received thrombolytic therapy with a regression of thrombus, and continued with immunosuppressive and anticoagulation therapy. Five months later, echocardiographic examination showed complete disappearance of thrombus.