The study was undertaken to identify determinants of health services' utilization related to organizational characteristics of the health services, social characteristics of the community, and health and socio-demographic characteristics of the population. We used a follow-up design involving a time dimension of 12 months. A cohort of 3000 50-year old males and females were randomly selected from an urban county near Copenhagen and a rural county in Western Jutland and 65% agreed to participate. Data were collected through: 1) mailed questionnaires to the participants every three months, 2) a mailed questionnaire to all general practitioners in the counties, and 3) the Health Insurance Register. Data were analyzed by multivariate logistic regression analysis. Utilization of health services was found to be strongly associated with gender and health characteristics, especially with respect to functional status and chronic diseases. Health service characteristics, demographic and psycho-social factors had very little impact on utilization patterns. The utilization of publicly financed health services was found to be determined by health needs rather than by social, psychological and organizational factors, indicating geographical and social equity in the access to the Danish health services.