OBJECTIVES: Schizophrenia and bipolar disorder (BD) are psychiatric disorders that are associated with a substantial clinical and economic burden. Hospitalization and in-patient care commonly account for a large proportion of medical costs in these illnesses. A secondary objective of the Italian Burden of Illness on Schizophrenia and BD (IBIS) study is to assess any differences in terms of cost of illness for patients with schizophrenia and BD switching from QTP-IR to QTP-XR. METHODS: Multicenter, retrospective, observational, real world cohort study (NCT01392482). The data shown are interim results collected from administrative databases in 6 of 20 Italian Local Health Units included in the study. Data were collected between 1 January 2009 and 31 December 2010. Patients that switched from QTP-IR to QTP-XR were included for analysis. Data were collected 6 months before (IR period) and 6 months after (XR period) the switch. RESULTS: In total, 213 patients switched medication from QTP-IR to QTP-XR (86 with schizophrenia, 127 with BD). For patients with schizophrenia, disease-related costs per patient totaled €4123 during the IR period and €3832 during the XR period, indicating a decrease of 7%. Although hospitalization costs per patient remained similar after the switch (IR period: €1111, 26.9% of total costs; XR period: €998, 26.0% of total costs), care/nursing home costs decreased in the XR period (IR period: €1906, 46.2% of total costs; XR period: €1330, 34.7% of total costs). For patients with BD, disease-related costs per patient decreased by 23%, from €3877 during the IR period to €2,973 during the XR period. Hospitalization costs per patient fell substantially after the switch (IR period: €2659, 68.6% of total costs; XR period: €1,171, 39.4% of total costs). CONCLUSIONS: These interim results suggest that switching from QTP-IR to QTP-XR decreases direct health care costs and in-patient resource use.