Fractal dimension () characterises the size distribution of low attenuation clusters on CT and assesses the spatial heterogeneity of emphysema that per cent low attenuation volume (%LAV) cannot detect. This study tested the hypothesis that %LAV and have different roles in predicting decline in FEV, exacerbation and mortality in patients with COPD.Chest inspiratory CT scans in the baseline and longitudinal follow-up records for FEV, exacerbation and mortality prospectively collected over 10 years in the Hokkaido COPD Cohort Study were examined (n=96). The associations between CT measures and long-term outcomes were replicated in the Kyoto University cohort (n=130).In the Hokkaido COPD cohort, higher %LAV, but not , was associated with a greater decline in FEV and 10-year mortality, whereas lower , but not %LAV, was associated with shorter time to first exacerbation. Multivariable analysis for the Kyoto University cohort confirmed that lower at baseline was independently associated with shorter time to first exacerbation and that higher LAV% was independently associated with increased mortality after adjusting for age, height, weight, FEV and smoking status.These well-established cohorts clarify the different prognostic roles of %LAV and , whereby lower is associated with a higher risk of exacerbation and higher %LAV is associated with a rapid decline in lung function and long-term mortality. Combination of %LAV and fractal may identify COPD subgroups at high risk of a poor clinical outcome more sensitively.