A prospective study of 419 patients aged 70 and over admitted to acute medical wards was carried out by medical staff from a geriatric unit. Data, including presenting problem, housing, social support, mental state, continence, and degree of independence before and after admission, were recorded. Of the 419 patients, 143 remained in hospital after 14 days and 65 after 28 days. The major factors associated with prolonged stay in hospital included advanced age, stroke, confusion and falls as reasons for admission to hospital, incontinence, and loss of independence for everyday activities. Social circumstances did not predict length of stay. Although these factors are interrelated, the most important influence on length of stay was the medical reason for admission. Early contact with the geriatric medical unit in these patients may speed up the recovery or result in more appropriate placement.