ABSTRACT: BACKGROUND:Community residential aftercare (step-down) services can ease the transition after a mental health hospital stay for patients with severe mental illness (SMI). AIMS:To investigate use of community and specialised mental health care services and costs in patients with SMI the first 12 months after discharge from a mental health hospital (MHH), comparing community residential aftercare (CRA) and treatment as usual. METHODS:An open parallel group randomised controlled trial with 41 participants. Data on use of specialist services (hospital, ambulant treatment and outpatient treatment) and community services (residential stays, home help, home care nursing, mental health consultation) were collected from specialist and community registers and health records. RESULTS:For the primary outcome, utilisation of community mental health services, the intervention group used, on average, 29% fewer hours (mean differences -?21.6 h, 95% CI -93.1 to 44.9, p?=?.096) with a cost saving of 29% (mean differences -?1845 EUR, 95% CI -8267 to 4171, p?=?.102), but the estimates were imprecise. For the secondary outcome, the study groups had the same total number of inpatient days (66 days), but the intervention group had on average of 13.4 fewer inpatient days in the mental health hospital (95% CI -29.9 to 0.9. p?=?.008). The number of inpatient admissions (mean difference?-?0.9 admissions, 95% CI -3.5 to 1.5, p?=?.224) and readmissions (-?0.8, 95% CI -2.5 to 0.9. p?=?.440) was lower in the intervention group. The intervention group had on average a total cost saving of 38.5% (mean differences -?23,071 EUR, 95% CI -45,450 to 3027. p?=?.057). A post hoc multivariable regression analysis controlling for baseline characteristics gave a reduction in total cost in favour of the intervention group of -?19,781 EUR (95% CI -44,072 to 4509, p=,107). CONCLUSION:In this study, it was not possible to draw a definite conclusion about the effect, due to the small sample and imprecision of the estimates. The direction of the results and size of the point estimate, in addition to findings in other studies, indicates that transferring patients ready for discharge from mental hospital to community residential aftercare can have the potential to reduce total consumption of health services and costs without increased hospital admissions. TRIAL REGISTRATION:Registered in clinicaltrials.gov ( NCT01719354 ).