To determine whether the adoption of the CONSORT checklist is associated with improvement in the quality of reporting of randomised controlled trials (RCTs). MEDLINE, EMBASE, Cochrane CENTRAL, and reference lists of included studies and of experts were searched to identify eligible studies published between 1996 and 2005. Studies were eligible if they (a) compared CONSORT-adopting and non-adopting journals after the publication of CONSORT, (b) compared CONSORT adopters before and after publication of CONSORT, or (c) a combination of (a) and (b). Outcomes examined included reports for any of the 22 items on the CONSORT checklist or overall trial quality. 1128 studies were retrieved, of which 248 were considered possibly relevant. Eight studies were included in the review. CONSORT adopters had significantly better reporting of the method of sequence generation (risk ratio [RR], 1.67; 95% CI, 1.19-2.33), allocation concealment (RR, 1.66; 95% CI, 1.37-2.00) and overall number of CONSORT items than non-adopters (standardised mean difference, 0.83; 95% CI, 0.46-1.19). CONSORT adoption had less effect on reporting of participant flow (RR, 1.14; 95% CI, 0.89-1.46) and blinding of participants (RR, 1.09; 95% CI, 0.84-1.43) or data analysts (RR, 5.44; 95% CI, 0.73-36.87). In studies examining CONSORT-adopting journals before and after the publication of CONSORT, description of the method of sequence generation (RR, 2.78; 95% CI, 1.78-4.33), participant flow (RR, 8.06; 95% CI, 4.10-15.83), and total CONSORT items (standardised mean difference, 3.67 items; 95% CI, 2.09-5.25) were improved after adoption of CONSORT by the journal. Journal adoption of CONSORT is associated with improved reporting of RCTs.