In contrast to attempts that have been made to measure the clarity of reporting of the methods of clinical trials in journal articles, we report here an attempt to measure the accuracy of methods reporting. We focus in this article on eligibility criteria as a test case for the reporting of clinical trial methods. We examined the reporting of eligibility criteria in the protocol, methods paper (if applicable), journal article, and Clinical Alert for articles appearing in print between January 1988 (...) and September 1994 for which a Clinical Alert had been issued. Eligibility criteria were further classified into five categories in order to examine the content of information loss, if any. On average, 82% of protocol eligibility criteria were reported in methods papers. Journal articles and Clinical Alerts fared somewhat worse: 63% of criteria were reported in journal articles, 19% in Clinical Alerts. In all three categories of medical communication, the reporting of criteria that defined the study disease tended to be complete; reporting of criteria relating to trial precision, patient safety, legal and ethical concerns, and administrative considerations, was not complete. We found that criteria for clinical trial eligibility are frequently under-reported in medical communications. Moreover, some of the criteria omitted are of considerable clinical importance. We suggest that in the design phase of clinical trials, proposed eligibility criteria be scrutinized closely. Those criteria that survive this scrutiny and that have clinical import must be reported upon fully and accurately when communicating trial results. (shrink)