Objectives: First, to investigate how many decisions by one commissioning body (district health authority) were based on evidence of effectiveness from randomised controlled trials (RCTs) and systematic reviews of RCTs. Second, to investigate whether other types of quantitative studies and qualitative studies could be used as evidence to support commissioning decisions. Method: From three planning documents (for 1997-1998), all statements were identified. Effectiveness questions were constructed from each and used to search for evidence from trials and reviews in the Cochrane Library (Issue 4, 1998). Further searches for other studies (all methodologies) were performed on a subset of decisions and appraised by an independent expert panel. Results: A total of 124 decisions were identified of which two-thirds concerned organisation of care. Evidence existed for less than half (48.4%) the decisions, with 33.9% favouring the decision and 14.5% where evidence was either equivocal or unfavourable. From a random subset of ten decisions, relevant non-randomised quantitative studies and qualitative studies were identified for half the decisions. Evidence from economic evaluations was identified for only one decision. Conclusions: Large gaps in knowledge exist if health care purchasers are to base their decisions on evidence of effectiveness from RCTs. However, other types of evidence can be used to support such decisions. Summaries of research should be published in a format that is accessible to purchasers.