Objective – The study aims to identify the predicting factors of hospitalization in patients who come in Emergency Room with psychiatric symptoms. Method – Cross-sectional study using data collected by E.R. of S.Gerardo Hospital in Monza from 1st of June 1995 to 31 May 1997. Inclusion criteria were age older than 18 and the need for psychiatric evaluation. The influence on disposition decision of demographic, clinical and service variables were assessed. Main outcome measures – Data were collected by a questionnaire designed for the study and administered by a trained psychiatrist. Statistical analysis was performed by univariate analysis and logistic regression. Results – 2076 cases were evaluated. Univariate analysis yielded higher odds of hospitalization for patients between 39 and 48 years of age, unmarried, unemployed, affected by schizophrenia, mood disorders or personality disorders. A linear trend was reported between hospitalization and severity of illness, siucide risk and aggressivness. While anxiety proved to be a protective factor, hallucination, delusion, lack of insight, psychomotor inhibition, agitation, confusion, destructive behaviour, odd behaviour, abnormal consciousness and previous hospitalization increase inpatient disposition. On Monday and Friday higher frequency of hospitalization was observed. Logistic regression confirm the role of age, symptoms, aggressive behaviour, severity of illness, suicide risk, and, among services variables, days of the week. Conclusion – Clinical variables proved to be the main predictors of hospitalization, and an important role is played by the availability of outpatients services: hospitalization was more frequent in the days closer the week-end, when the outpatient services are closed.