PURPOSE: To assess the extent to which relevant controlled clinical trials are cited and summarized in review articles, and to determine whether citation of relevant clinical trails is biased as to study results. DATA SOURCES: Articles were identified by searching MEDLINE and EMBASE databases. STUDY SELECTION: Review articles published between 1986 and 1988 on the clinical effectiveness of pneumococcal vaccine. DATA EXTRACTION: Proportion of relevant clinical trials cited and whether citation is biased by study results. DATA SYNTHESIS: The proportion of relevant primary studies cited per review article ranged from 0% to 36% (mean 9%). The number of trials cited per review ranged from zero to six (mean 1.2). In nine of 17 reviews, no clinical trials were cited. Study populations and outcome(s) were specified and results presented quantitatively for 0 to 27% of relevant trials per review (mean 6%). Unsupportive trials were almost twice as likely to be cited as supportive trials. CONCLUSIONS: Reporting of the results of relevant clinical trials in reviews of pneumococcal vaccine effectiveness is incomplete. Our findings suggest a need for greater scientific rigour in preparing, reviewing, and editing review articles.