BACKGROUND: In workplace respiratory disease prevention, a thorough understanding is needed of the relative contributions of lung function loss and respiratory symptoms in predicting adverse health outcomes. METHODS: Copenhagen City Heart Study respiratory data collected at 4 examinations (1976-2003) and morbidity and mortality data were used to investigate these relationships. With 15 or more years of follow-up for a hospital diagnosis of chronic obstructive pulmonary disease (COPD) morbidity, COPD or coronary heart disease (CHD) mortality, and all-cause mortality, risks for these outcomes were estimated in relation to asthma, chronic bronchitis, shortness of breath, and lung function level at examination 2 (1981-1983) or lung function decline established from examinations 1 (1976-1978) to 2 using 4 measures (FEV(1) slope, FEV(1) relative slope, American College of Occupational and Environmental Medicine's Longitudinal Normal Limit [LNL], or a limit of 90 milliliters per year [ml/yr]). These risks were estimated by hazard ratios (HR) and 95% confidence intervals (CI) adjusted for age, height-adjusted baseline forced expiratory volume in 1 second (FEV(1)/height(2)), and height. RESULTS: For COPD morbidity, the increasing trend in the HR (95% CI) by quartiles of the FEV(1) slope reached a maximum of 3.77 (2.76-5.15) for males, 6.12 (4.63-8.10) for females, and 4.14 (1.57-10.90) for never-smokers. Significant increasing trends were also observed for mortality, with females at higher risk. CONCLUSION: Lung function decline was associated with increased risk of COPD morbidity and mortality emphasizing the need to monitor lung function change over time in at-risk occupational populations.