A patient with a history of transient cerebral ischemic episodes had two-dimensional echocardiographic findings consistent with mitral stenosis associated with a spherical free-floating left atrial thrombus. The patient was operated on in the next few days, performing a mitral commissurotomy, and the left atrial thrombus was removed, without intra- or postoperative complications. The patient was discharged from the hospital on an antiplatelet drug regimen. Free-floating left atrial thrombi are a very rare finding with an easy echocardiographic diagnosis. Prompt surgical treatment is mandatory because the risk of systemic embolization and sudden death are inherent in this entity.