Objective - The analysis aims to study trends, during the period of 1983-1993, of the most relevant variables concerning equipment, staff and activity of the Lombardy Region Psychiatric Services. Setting - The study used data from all services, both hospital and community, that depend on Psychiatric Units. Data regarding Psychiatric Hospitals were not included. Design - Data were provided by the Regional Psychiatric Information System, which since 1983 has regularly collected information on equipment, staff and services supplied by the Regional Psychiatric Unit. A graphic analysis with a description of trends and the interrelation of the time series has been carried out. Main outcome measures - The analysis uses two types of variables: resources and services variables related to other community psychiatric facilities. Indexes or rates are computed to study the relations between the two sets of variables. Results - We verified a remarkable upward trend in the level of activity (both hospital and community) not entirely explained by the increase in resources. In fact, the growth of psychiatric services is linked with higher productivity and a growing demand as well. We have also seen that the growth of community activity has been stronger than that concerning hospital variables. Thus, as far as we can assess from data (not including the private sector), the use of hospitalization in psychiatric activity has decreased in the last decade. Conclusions - The analysis highlights the importance of an Information System to describe changes in service organizations and to provide data for specific studies, such as outcome studies.