We provide new evidence on the effects of workplace smoking restrictions by studying more than 100 local smoking ordinances in Ontario, Canada from 1997-2004. We advance the literature by examining local (as opposed to state or provincial) laws in a quasi-experimental framework and by explicitly testing for effects on worksite compliance and exposure to environmental tobacco smoke (ETS). We show that the local laws significantly increased workplace smoking restrictions for blue collar workers, and among this group the laws (and, by implication, workplace smoking bans) reduced ETS exposure by 28-33 percent. We find smaller and insignificant estimates for other workers. (Contains 4 tables, 4 figures and 26 footnotes.)