Haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are conditions in which thrombocytopenia and microangiopathic haemolytic anaemia are associated with organ damage due to thrombotic microangiopathy (TMA). The prognosis for adults with HUS is variable, with some patients presenting with an acute illness from which a full recovery is made, whilst others develop irreversible renal failure. Evidence of retinal ischaemia was noted on presentation in a normotensive patient with irreversible renal failure due to HUS. This study examined prospectively the optic fundi of all patients who subsequently presented to a single adult renal unit (catchment population approximately 700,000) with HUS. Eleven patients presented with HUS over 12 years (1985-1997). Six patients with irreversible renal failure had retinal abnormalities either at the time or within a few days of initial presentation. The other five patients whose renal function recovered did not develop retinal changes during the course of their illness. Retinal ischaemia associated with TMA is a poor prognostic sign in adults with HUS.