The aim of this study was to examine the association between chronic mucus hypersecretion, and FEV1 decline, and subsequent hospitalization from chronic obstructive pulmonary disease (COPD). We used data from The Copenhagen City Heart Study on 5,354 women and 4,081 men 30 to 79 yr of age with assessment of smoking habits, respiratory symptoms, and spirometry at two surveys 5 yr apart. Information on COPD hospitalization during 8 to 10 yr of subsequent follow-up was obtained from a nationwide register. Chronic mucus hypersecretion was significantly associated with FEV1 decline; the effect was most prominent among men, where chronic mucus hypersecretion at both surveys was associated with an excess FEV1 decline of 22.8 ml/yr (95% confidence interval, 8.2 to 37.4) compared with men without mucus hypersecretion, after adjusting for age, height, weight change, and smoking; in women, the excess decline was 12.6 ml/yr (0.7-24.6). Chronic mucus hypersecretion was associated with subsequent hospitalization due to COPD after adjusting for age and smoking; relative risk was 5.3 (2.9 to 9.6) among men and 5.1 (2.5 to 10.3) among women. After further adjusting for FEV1 at the second survey, the relative risk was reduced to 2.4 (1.3 to 4.5) for men and 2.6 (1.2 to 5.3) for women. Chronic mucus hypersecretion was significantly and consistently associated with both an excess FEV1 decline and an increased risk of subsequent hospitalization because of COPD.