Over a 3-month period all adults presenting to the Accident and Emergency Department of St Mary's Hospital, Paddington, London, England, with a pyrexia of 37.6 degrees C or more were entered into this study. A questionnaire was used to document the incidence of pyrexia, the age, sex, specific diagnosis and the subsequent management of pyrexial patients. A total of 11,062 adults came through the Department during this time, of whom 834 (7.5%) were admitted. One hundred and eight-eight adults had a pyrexia of 37.6 degrees C or greater and, of these, 62 (33%) were admitted. Seventy-two per cent of patients aged 45 years or older were admitted, compared with 22% in the younger age groups. These results were statistically significant for the correlation between likelihood of admission and age. This study demonstrates that, for patients presenting to an accident and emergency department, pyrexia is a useful indicator of illness which may necessitate admission, especially in the elderly.