Rationale: Individuals who will develop chronic obstructive pulmonary disease (COPD) could be identified at an early age before clinical manifestations appear.

Objectives: We investigated risk of clinical COPD 10 years later in young adults from the general population with and without early COPD with a focus on smoking exposure.

Methods: We included 14,870 individuals aged 20-100 years from the Copenhagen General Population Study with spirometry 10 years apart. Early COPD was defined as baseline FEV1/FVC less than the lower limit of normal in individuals aged

Measurements and Main Results: Among 5,497 individuals aged = 0.70, 104 (3%) developed clinical COPD 10 years later; 4% of smokers with >= 10 pack-years had early COPD; 3% of smokers with = 10 pack-years, 24% developed clinical COPD in those with early COPD versus 4% in those without early COPD. Corresponding numbers were 10% and 1% in smokers with = 10 pack-years and 8.56 (95% CI, 4.92-14.9) in all smokers, whereas hazard ratios for acute exacerbation hospitalizations were 4.16 (95% CI, 1.66-10.5) and 4.33 (95% CI, 1.89-9.93), respectively. Results were validated in the Copenhagen City Heart Study.

Conclusions: Depending on amount of smoking exposure,