The Trial Criteria in Schizophrenia Working Group was convened in November 2007 to define consensus criteria for clinical trials in patients suffering from acute schizophrenia with special focus on placebo-controlled trials and withdrawal conditions. Clinical trials involving patients give rise to ethical and medico-legal dilemmas. Essential research of new drugs may potentially expose patients to ineffective treatment regimens or placebo. The complexity of the problem increases when dealing with mentally ill patients. The Working Group's criteria are thought to cover different aspects important in conducting clinical trials namely to ensure the patient's safety, to present criteria that would allow the ethics committees to agree to the proposed criteria and to enable the possibility to reasonably conduct and ensure comparable quality of clinical studies in acutely ill patients with schizophrenia. To furthermore counteract current inconsistencies, these criteria should be evaluated using standardized rating scales applying established cut-off criteria. The developed trial criteria cover inclusion and exclusion criteria as well as withdrawal criteria due to non-response or worsening of symptoms.