Background: Little information exists concerning the amount of information patients expect from physicians as to the risk for an adverse medication reaction. The present study was designed to determine such opinions in a population sample: to correlate results with sex, age, educational level, and previous experience with adverse effects; and to determine whether patients believe physicians should use discretion in the amount of such information given. Methods: Two thousand five hundred sequential adults visiting outpatient clinics filled out a 12-item questionnaire. Percentages of subjects desiring information about varying degrees of risk and those believing physicians should and should not use discretion in the amount of such information provided were recorded. Results were correlated with demographic variables and previous experience of adverse effects. Results: Among the respondents, 76.2% desired to be told of all possible adverse effects; 13.3% only if an adverse effect occurred 1 in 100000 times: and 10.2% only if such occurrence was 1 in 100 times; 0.4% were not interested in any information. (Percentages have been rounded and do not total 100.). Percentages were closely similar to those for the same question that restricted opinion to serious adverse effects. Desire for maximum information was significantly correlated with lower educational level (P<.001) and previous frequent experience with adverse effects (P<.001) and in older women (P<.001). The opinion that the physician should give the same information to all patients was given by 67.6% of the sample, and 73.4% opined that physicians were never justified in withholding any information. Conclusion: Most individuals desire from physicians all information concerning possible adverse effects of prescribed medication and do not favor physician discretion in these decisions.