The aim of this study is to clarify the potential benefits, disbenefits and costs of Orlistat for the treatment of obesity. The method was a search for relevant systematic reviews and randomized controlled trials, in Medline, Pre-Medline, Embase and the Cochrane Library, using Orlistat and its synonyms. Identified trials were appraised using a standard appraisal checklist and trial data were extracted for use in cost-effectiveness modelling. Three large multicentre, randomized placebo controlled trials were included in the rapid review. On average, Orlistat results in obese people losing an additional 3-4% of their initial body weight over diet alone during a 2 year period. There was no strong evidence that this short-term weight loss would have a longer-term impact on morbidity and mortality. The cost utility of Orlistat treatment was estimated at around 46,000 Pounds per Quality Adjusted Life Year gained (extreme values sensitivity analysis 14,000 Pounds to 132,000 Pounds). This rapid review raises some important questions about the potential value of Orlistat in the treatment of obesity. Further research is needed, not only to clarify the longer-term impact of Orlistat treatment, but also to uncover the longer-term impact on mortality and morbidity from short-term weight loss.