A unique situation found in two Utah counties has made it possible to estimate the fraction of respiratory cancer and nonmalignant respiratory disease (NMRD) deaths, which are attributable to community air pollution (CAP) in one county. The two counties were very similar in many ways, including low smoking rates, until a steel mill constructed during WW II caused substantial CAP in one of them. Subsequent differences in mortality rates from both respiratory cancer and NMRD are striking. A third county, similar to many counties outside Utah, was included in the analysis for comparison. In one county, 30-40% of the respiratory cancer and NMRD deaths were attributable to CAP. In this county, NMRD deaths (but not respiratory cancer deaths) were slightly more frequent than in Salt Lake County where smoking rates were twice as high.