To examine fluctuations in numbers of patients on surgical wards the dates of admission from January of each of the 5556 patients admitted from 1 January 1985 to 31 December 1987 were examined during computerised audit of a single surgical firm. The numbers of patients under the care of the firm fluctuated widely, often exceeding the 38 beds nominally available. Duration of stay varied from two days or less (3062 admissions) to more than a month (163 admissions). One patient was in hospital for 278 days. The patients admitted for more than a month (2.9% of the total) filled 28% of the beds; not all these patients were elderly. A further increase in throughput of patients undergoing elective operations might be achieved by always admitting patients on the day of operation, and perhaps by discharging patients even sooner than at present. Efficiency would increase but so would overall costs.