A girl with failure to thrive and a haemoglobin of 140 g/l at 1.3 years died from a brain haemorrhage 2.5 years later. Renal artery stenosis had caused severe, chronic hypertension and increased erythropoietin secretion (haemoglobin 182 g/l). Blood pressure should be measured in all unwell children, including those failing to thrive.