A particularly difficult challenge for treatment of people with serious mental illnesses in the community is the delivery of an acceptable level of care during the acute phases of severe mental illness. Crisis intervention models of care were developed as a possible solution to this problem. To review the effects of a crisis intervention model for anyone with serious mental illness experiencing an acute episode, compared to 'standard care'. Relevant randomised trials were identified by searching Biological Abstracts (1985-1998), CINAHL (1982-1998), The Cochrane Library, the Cochrane Schizophrenia Group's Register of trials, EMBASE (1980-1998), MEDLINE (1966-1998), PsycLIT (1974-1998), sociofile (1974-1998) and the ISI database (Science Citations and Social Science Citations). Further references were sought from published trials and their authors. All randomised controlled trials of crisis intervention models (however defined) versus standard care for people with severe mental illnesses (however diagnosed). Reviewers evaluated data independently and analysed on an intention-to-treat basis. Reviewers assumed that people who left the study early or were lost to follow-up had no improvement. Where possible and appropriate odds ratios (OR) and their 95% confidence intervals (CI) were calculated. The number needed to treat (NNT) was estimated. For continuous data Weighted Mean Differences (WMD) were calculated. Data were inspected for heterogeneity. None of the five included studies investigated 'crisis intervention' in a pure form. They all used a form of home care for acutely ill people, which included elements of crisis intervention. Despite its ethos, 45% of the home care group were unable to avoid hospital admission during their treatment period. Home care, however, was slightly superior in avoiding repeat admissions (OR 0.63 CI 0.42 - 0. 94), although this result is not robust due to significant heterogeneity. Other results suggest home care reduces loss to follow-up at six and 12 months (OR 0.62, CI 0.42-0.91, NNT 12, CI 6-53; OR 0.65, CI 0.44-0.96, NNT 13, CI 7-130 respectively), reduces family burden (OR 0.20, CI 0.10-0.42, NNT 3, CI 1-5), and is a more satisfactory form of care for both patients and families. No differences in loss, death or mental state were found suggesting home care is as effective as hospital care for these outcomes. All studies found home care to be more cost effective than hospital care but all data were either skewed or unusable. No data on staff satisfaction, carer input, compliance with medication and number of relapses were available. It is difficult to draw any robust conclusions from the data presented in this review. It is also difficult to comment on the effectiveness of crisis intervention in its pure form (i.e. specific results for the acute phase of mental illness only). Overall the review suggests that home care crisis treatment, coupled with an ongoing home care package, is a viable and acceptable way of treating people with serious mental illnesses. Other reviews of more clinically effective home care packages have had similar but more robust results and this review can give tentative support to their findings ( approximately approximately Marshall 1999 approximately approximately ). However, if a pure form of crisis intervention policy is to be specifically practised or implemented it would be hard to justify this outside of a simple well-designed trial. The reviewers also suggest that issues such as staff satisfaction and burnout would be important outcomes to consider in future research.