Objective – The aim of the study was to show, trough the calculation of the direct costs of supports and treatments actually provided by a NHS Mental Health Department, the presence of associations between four diagnostic groups (schizophrenia, affective psychosis, paranoia and neurotic disorders) and their overall and items (community care, rehabilitation facilities and in-patients services) costs. Setting – Mental Health Department and CSM “Scalo” (NHS Mental Centre), AUSL “Citta di Bologna”, Emilia-Romagna Region. Design – Yearly direct costs were calculated for a sample (n = 75) of all patients (N = 745) who during 365 days had more than four contacts with CSM and also for four randomised diagnostic groups (n = 30 per group). Main outcome measures – We calculated unit costs of 15 types of services provided by CSM, selected according to the yearly number of services provided and the time spent by each health professional, and the in patient-cost per all days spent in a public or private sector hospital for psychiatric care. Results – The statistic analysis, performed with the help of the Kruskal-Wallis test, showed significantly higher overall costs for the schizophrenic patients than the sample-group and the neurotic disorders-group; besides a significant difference in the item costs for rehabilitation facilities was found between the schizophrenic group and the paranoia, neurotic disorders groups and the sample one, whereas no significant differences in costs of inpatients services and drugs administration were tested between the groups. Conclusions – The results of our study allow to demonstrate that there are cost differences between the diagnosis (direct costs are highest for schizophrenic patients and lowest for those with neurotic disorders) and that the costs evaluation can be used to ensure appropriate provisions to Mental Health Department for support and treatment of a wide range of psychiatric disorders.