Background Data on effectiveness of acute dayhospital treatment for psychiatric illness are inconsistent. Aims To establishthe effectiveness and costs of care in a dayhospitalproviding

Declaration of interest None. Fundingdetailed in Acknowledgements. A recent survey reported 102 psychiatric services in England describing themselves as ‘acute day hospitals’; 66% of these services rated the provision of an alternative to acute in-patient care as being of ‘great’ or ‘greatest importance’ to their service (Briscoe et al, 2004). A systematic review of randomised controlled trials of day hospitals concluded that day hospital treatment is generally cheaper and associated with greater treatment satisfaction than in-patient treatment (Marshall et al, 2001). However, findings on improvements in psychopathology are inconsistent and reviews agree that more primary research on the efficacy of day hospital care is needed (Hortwitz-Lennon et al, 2001; Marshall et al, 2001). We conducted a randomised controlled trial comparing conventional in-patient care with treatment in a day hospital that exclusively provides an acute service as part of a modern community mental healthcare system.