Objective - The aim of the present paper is to assess the supply and demand of psychotherapy in mental health services and to identify the factors predicting the start of psychotherapy, using routine data, including 18 clinic and extraclinic variables, collected at 10 Mental Health Centers. Setting - Ten Mental Health Services of Regione Emilia-Romagna. Design - A prospective longitudinal study regarding all «new» users in 1995 followed for one year after the first visit. Results - The percentage of the new users starting a psychotherapy was 11.5%, corresponding to an overall one-year incidence of 5.6/10000 inhabitans ≥18 years old (range 0.9-14.8 across the 10 centres). The demand of psychotherapy in 1995 was 16.1%, including both the request of the patients and the primary care physicians (range 0.6-33%). The predictive factors for the beginning of the psychotherapy were: the presence of a psychologist at the first encounter, the request of the patient for a psychotherapy, age < 48 years, high educational level, being student, living with the family, the Mental Health Center; the broad diagnostic group of «neurotic» diagnoses resulted to have a twofold probability with respect to controls to start a psychotherapy. The logistic regression analysis of 18 variables coudn't find a predictive model with more than 33% sensitivity. Conclusions - The psychotherapeutic treatment is not predictable in the 10 Centers we studied, because of extreme differences in psychotherapy supply among Centers and probably because of uncertainty of therapeutic recommendations for psychotherapies.