Accessory mitral valve tissue is an extremely rare congenital cardiac anomaly. Most of the cases reported in the medical literature were associated with left ventricular outflow tract obstruction. The majority of cases of accessory mitral valve tissue, causing left ventricular outflow tract obstruction, occur in association with other congenital cardiac anomalies. In this reported case, a patient with accessory mitral valve tissue complicated with thromboembolic cerebrovascular event is presented. The patient also had an associated idiopathic hypertrophic subaortic stenosis. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.