BACKGROUND: People suffering from acute psychotic illnesses, especially those associated with agitated or violent behaviour, may require urgent pharmacological tranquillisation or sedation. Droperidol, a butyrophenone neuroleptic, has been used for this purpose in several countries. OBJECTIVES: To estimate the effects of droperidol compared to other treatments for controlling disturbed behaviour and reducing psychotic symptoms for people with suspected acute psychotic illnesses. SEARCH STRATEGY: We updated previous searches by searching the Cochrane Schizophrenia Group Register (September 2003). References of all identified studies were searched for further trial citations and authors of trials were contacted. Twenty-one other databases were also searched as part of a broader project and this composite database was searched for this review. This was supplemented by hand searching reference lists and contacting both the pharmacological industry and relevant authors. SELECTION CRITERIA: The review included randomised controlled trials comparing droperidol to any other treatment for people with suspected acute psychotic illnesses, including schizophrenia, schizoaffective disorder, mixed affective disorders, the manic phase of bipolar disorder or a brief psychotic episode. DATA COLLECTION AND ANALYSIS: Relevant studies were selected for inclusion, their quality was assessed and data extracted. Data were excluded when more than 50% of participants were lost to follow up. For binary outcomes, standard estimates of risk ratio (RR) and the corresponding 95% confidence intervals (CI) were calculated. Where possible, weighted number needed to treat or harm statistics (NNT, NNH), and the corresponding 95% confidence intervals (CI), were calculated. MAIN RESULTS: We identified only two relevant trials. One additional study focused on outcomes at 30 days rather than at a few hours. One small (n = 41) randomised trial compared intravenous (iv) droperidol (10 mg) with iv placebo and found that people allocated to droperidol were significantly less likely to need additional injections of another drug, haloperidol, in the first few minutes (n = 41, RR 0.37 CI 0.2 to 0.7, NNT 2 CI 1 to 10) compared to those given placebo. By 90 minutes this difference was still evident but not statistically significant (RR 0.46 CI 0.2 to 1.2). When 5 mg intramuscular (im) droperidol was compared with 5 mg im haloperidol, those given droperidol were also less likely to need additional injections by 30 minutes, than those given haloperidol, but this result was not statistically significant (n = 27, RR 0.45 CI 0.2 to 1.01). One person out of the 16 given haloperidol experienced a mild dystonic reaction (muscle spasms or abnormal contractions), while none of the 11 people allocated to droperidol were reported to have experienced adverse effects. REVIEWERS' CONCLUSIONS: This is an important, and surprisingly under-researched, area. To date, use of droperidol for emergency situations has been justified by experience rather than evidence from well conducted and reported randomised trials, but, as world reserves diminish, droperidol will no longer be a treatment option.