A 54 year old man presented with presyncopal symptoms. Echocardiography and subsequently computed tomography showed a mass in the posterior mitral annulus causing incompetence of the valve. At operation a lipoma was found which could not be resected. Mitral incompetence was the result of chordal rupture where the lipoma had engulfed the papillary muscle. The valve was replaced and the patient made an uneventful recovery. This case report shows a potential danger of an otherwise benign lesion.