We assessed the factors associated with hospital admission in Ontario, Canada, across age-specific and sex-specific groups. Data from the cross-sectional, population-based 1990 Ontario Health Survey (OHS) were used to examine the relationships between hospital admission and sociodemographic, health care need, psychosocial, and lifestyle factors. The OHS sample of 42,698 adults aged > or = 16 years, weighted to represent more than 7 million Ontarians, was used. Hospitalization rates per 1000 in the prior year were 130 for men and 203 for women. The higher rates for women are attributed in part to admissions related to childbearing. Women who delivered a child in the year before the OHS were excluded from subsequent analyses. Multivariate logistic regression models revealed that health care need (increasing number of health problems, fair/poor health status, older age) was the most important factor associated with higher hospitalization rates for men. For women, in addition to health care need, psychosocial (low/average well-being) and sociodemographic factors (married, low income, unemployed, English/French spoken in the home) were related to higher hospital utilization. Health care need is the most important factor for describing hospital use in men and women. However, rates of hospital utilization for women are more sensitive to sociodemographic factors even in a setting with universal health insurance. This suggests that among women, societal factors may exist that relate to potential disparities in access to health services. Efforts to assess how these factors operate are necessary to aid the development of interventions to minimize disparities that may exist.