OBJECTIVE: To describe the length of stay, cost of drug treatment, diagnostic tests and other therapeutic measures in acute psychotic patients admitted to acute in-patient psychiatric units and to analyse the factors associated with these. METHODS: Retrospective review of medical records of 200 patients admitted for acute psychosis in 8 Spanish hospitals. Description of the length of stay, cost of drug treatment and diagnostic tests; bivariate and multivariate analysis of factors associated with length of stay and cost of antipsychotic drug treatment. RESULTS: The average admission cost ranged between €2,830.29 and €3,624.95, with a wide variability among hospitals. Of this cost, 94.3% corresponded to fixed costs, 3.4% to diagnostic tests and 2.4% to drug treatment (84.2% of this latter cost corresponded to antipsychotic drugs). An age younger than 25 years and a diagnosis of schizophrenia were associated with longer hospital stays; longer length of stay, the presence of aggressiveness/agitation, a diagnosis of schizophrenia, age younger than 25 years and the use of atypical antipsychotics were associated with higher costs in antipsychotic drug treatment. CONCLUSIONS: The hospital admission cost of an acute psychotic episode is mostly dependent on the structural costs derived from in-patient treatment. The differences in costs seem to be related to different length of stay schemes used by the various hospitals rather than to the clinical characteristics of patients or the drugs used.