Raad et al2 conducted two separate meta-analyses on six eligible cross-sectional studies comparing lung function between water-pipe smokers and nonsmokers and water-pipe smokers and cigarette smokers, respectively. The six included studies were selected on the basis of standardized criteria after review of >1,600 published works on WPS. Three spirometric measurements (FEV1, FVC, and FEV1/FVC) were examined, and the standardized mean difference was used to pool results. A significant decrease in the FEV1, equivalent to a 4.04% lower FEV1% was found in the WPS group compared with the nonsmokers, as was a trend (nonsignificant) toward a lower FVC and FEV1/FVC. No difference was found in FEV1, FVC, or FEV1/FVC between the WPS and cigarette-smoking groups. The authors conclude that the significant decrease in FEV1 among water-pipe smokers not only is clinically relevant in terms of minimal important difference but also supports a possible role for WPS in the development of COPD. The lack of difference between cigarette smokers and water-pipe smokers suggests that WPS may be as deleterious to lung function as cigarette smoking. There are significant methodologic issues in the component studies of the meta-analysis, which the authors acknowledge, and an association drawn from this analysis of cross-sectional data does not establish causation. Yet, given the biologic plausibility of an adverse effect of WPS on lung function and other data supporting a link between WPS and chronic bronchitis,4 it is highly likely that WPS causes COPD.