To describe the demographic, social and medical morbidity and usage of health services of the population of single homeless individuals in Sheffield, a census was carried out over a 12-hour period at sites which homeless people frequent, as identified by those who work with the homeless. These sites included Salvation Army hostels, reception centres, probation day centres, voluntary organisation hostels, and cheap bed and breakfast accommodation. Data were collected by means of a self-administered questionnaire. A total of 340 single homeless individuals were studied, constituting 80-90% of the single homeless population of Sheffield, as estimated by field workers. The population was younger than those of earlier studies and contained a higher proportion of females (14%). One-fifth of the population had been homeless for less than six months, and 60% had been at their present lodging for less than six months. The population has a higher proportion of both ex-prisoners (49%) and ex-inmates of psychiatric hospitals (36%). Over a quarter admit to a history of alcoholism, and 9% to a history of drug abuse; 65% of the population are registered locally with a GP, and 53% of the population see their GP. Those who are more likely to use an Accident and Emergency Department are less socially integrated and more likely to be alcoholic. This study of the single homeless highlights a need for social change to reduce poverty, provide cheap available housing and provide support for disadvantaged groups.