We describe a 42-year-old woman who developed lichen myxoedematosus. Twenty years after the onset of the disease she became breathless and hypertensive, and an echocardiogram showed a mass on the mitral valve, which was thought to be a mucin deposit. Her hypertension was resistant to treatment with combination antihypertensives. To our knowledge, this is the first report to link lichen myxoedematosus with a valvular mucinous mass. This case also demonstrates the slow clinical progression of the disease over 20 years.