A health economics study was carried out from 1995 – 1997 on the public sector of psychiatry in order to explore the variables which contribute to the differences in the cost of psychiatric care. The results show that the costs are independent of the pathology, but they correlate to the level of medical-social dependence and to the existence (or not) of family and social support structures. The most expensive care per year is that of patients diagnosed with dementia, intellectual deficiencies, or problems of schizophrenia. If the sociological variables of sex, age and professional category are highly significant in the redistribution of cost, these are independent of the quality and provision of care, measured by a comprehensive, overall operational scale (EGF). 10% of patients consume 75% of the available resources but only 50% of the ambulatory care. The definitive costs are ultimately influenced by hospitalization. The increase in the number of patients actively seeking treatment and the increase in ambulatory care provided levels out year after year for which there is a noted decrease in full time hospitalization. Regardless of the diagnosis, full time hospital care carries the same cost. Therefore, the 10% of patients for whom care is most expensive are those who have been diagnosed with CIM 10, schizophrenic patients representing less than half of them.