The prevalence of visual impairment among elderly patients admitted to hospital is unknown. This group of patients may be particularly at risk from poor vision which could jeopardise their independence. A prospective study of visual imapairment and its aetiology in acute geriatric admissions assessed after the acute illness had settled was performed. Subjects were all patients aged 65 years or over, excluding those chronically confused, admitted to the Department of Geriatric Medicine at the Royal Liverpool University Hospital with an acute medical illness. After the acute illness had settled visual impairment, as defined by the American criteria (best acuity 6/18), was assessed on the ward with a Snellen chart read at 6 m using binocular vision and current glasses. Those patients identified with impaired vision on initial screening were formally assessed in the ophthalmology department to identify the cause. 200 patients were examined. 101 patients (50.5%) had impaired vision. In these patients, correctable refractive errors were present in 40%, cataract in 37% and senile macular degeneration in 14%. Of the 101 patients with impaired vision 79% had a reversible cause. Comparing these results with a recent study in the community showed a much higher incidence for patients admitted to hospital. There was a particularly high prevalence in those elderly patients who were admitted with falls (76%, p = 0.0003). In conclusion, elderly patients, especially those presenting with falls, admitted to hospital have a high prevalence of visual impairment. Visual impairment may be compounding or causing falls.(ABSTRACT TRUNCATED AT 250 WORDS)