The aim of this report is to call attention to a poorly recognised cause of pulmonary hypertension, thiamine deficiency. A 78-year-old woman without alcoholism or malabsorption presented with progressive dyspnoea and generalised oedema. Echocardiography showed signs of right ventricular overload with an estimated systolic pulmonary artery pressure of 50 mm Hg. Increased lactate concentrations prompted us to investigate thiamine deficiency. A 3-month history of picky eating, relying exclusively on white rice as the staple food, and low blood concentrations of thiamine confirmed the diagnosis. She recovered fully after 12 days of intravenous thiamine administration. Thiamine deficiency should be considered in all patients with pulmonary hypertension of unknown origin.