We report the results of a ban on smoking in The Johns Hopkins Children's Center, Baltimore, Md, beginning in July 1987. A survey 6 months before and 6 months after implementation of the ban showed current smoking prevalences to be 15% and 13.8%, respectively. The percentage of smokers who smoked at work declined from 82% before the ban to 43% after the ban. After the ban, 66% of smokers and 93% of nonsmokers agreed that a hospital should be smoke free, while 43% and 83%, respectively, agreed with this statement before the ban. Systematic observations showed a decline from 53% of visitors and staff smoking in public areas 1 month before the ban to 0% smoking 6 months after the ban. Twenty-four-hour cigarette butt counts in elevator lobbies located well within the center dropped from 940 for an average day to 19 for an average day 6 months after the ban. Finally, measurement of environmental nicotine vapor showed a decline from a weekly average concentration of 13 micrograms/m3 of nicotine 1 month prior to the ban to 0.51 micrograms/m3 of nicotine 6 months after the ban in nine lobby lounges. The results suggest that a total ban on smoking in a hospital is feasible and effective in virtually eliminating public smoking.