Randomized controlled trials of herbal interventions underreport important details of the intervention. 
To examine the quality of reporting and predictors of reporting in randomized clinical trials (RCTs) of herbal medicine interventions.  We searched Medical Literature Analysis and Retrieval System Online, Excerpta Medica Database, and Academy of Microscope Enhanced Dentistry up to December 2007 for any English language RCT of 11 commonly used herbal medicine interventions.  Two individuals separately and independently assessed all trials using the Consolidated Standards of Reporting Trials (CONSORT) checklist for herbal medicines interventions.  We randomly selected 100 of these trials, extracted a set of potential predictor variables identified through a literature search and consultation with experts, and performed a conceptually driven stepwise elimination regression analyses for predictor variables.  The 406 trials reported on average 38% of the information suggested in the checklist.  Regression analyses revealed better overall reporting in trials with a participant flow diagram (P=0.008), those of Panax quinquefolius (P=0.018), and those published in more recent years (P=0.02).  Our results indicate that RCTs of herbal medicine interventions frequently do not report important characteristics of the intervention.  Trialists should refer to the CONSORT for herbal medicines when reporting their trials.