Smoking is a major modifiable risk factor in pregnancy, and low-cost interventions have been developed and tested in diverse populations of pregnant smokers. Successful intervention depends on identification, however, and nondisclosure can be a problem. This randomized study compared rates of disclosure with two response formats--multiple choice, in which the patient is able to describe herself as having "cut down," and the usual history question, "Do you smoke?," in which she is forced to answer simply "yes" or "no". Each format was tested in both oral and written channels with a multiethnic adult prenatal population (n = 1078) entering care in a multispecialty group. Study results indicate that the multiple choice question improved disclosure, regardless of channel (oral versus written), by 40%. This effect was observed across racial and ethnic groups. Biochemical tests of urine samples from reported nonsmokers indicated smoking in only 3%. Eleven percent of the "nonsmokers" in the experimental groups refused consent for the urine test, however, and many of these were probably smokers.