Recent re-evaluation of preventive health care has resulted in more limited and directed guidelines; nonetheless, physician compliance has remained poor. This study assessed whether an inexpensive reminder system of preventive care checklists would improve physician implementation of periodic health measures. Residents in internal medicine were randomly placed into two groups: one received a copy of the appropriate checklist with each patient's medical record; the other did not. After one year, 200 randomly selected records were audited to determine the proportion of recommendations implemented for each patient. Residents who received checklists performed appropriate preventive health measures at a significantly higher rate than those who did not (0.56 +/- 0.26 versus 0.39 +/- 0.22, p less than 0.002). The actual use of the checklist to record the results was associated with an even higher rate of compliance compared with instances in which the checklists were provided but not used and instances in which checklists were not received (0.70 +/- 0.21 versus 0.44 +/- 0.24 and 0.39 +/- 0.22, respectively, p less than 0.002). These data suggest that a physician's use of simple checklists can provide an inexpensive and effective means of improving implementation of periodic health maintenance.