"High risk" groups for exacerbations of chronic obstructive pulmonary disease (COPD) in the 2011 Global Initiative for Chronic Obstructive Lung Disease (GOLD) proposal (i.e. groups C and D) [1] include: patients with a forced expiratory volume in 1 s FEV1 <50% reference and <2 exacerbations year-1 (subgroups C1 and D1); patients with ≥2 exacerbations·year-1 and an FEV1 ≥50% reference (subgroups C2 and D2); and patients with both FEV1 <50% ref. and ≥2 exacerbations·year-1 (subgroups C3 and D3) [2–5]. We hypothesised that these high-risk subgroups will differ in other clinical, functional and biological characteristics and will be associated with different long-term outcomes. We explored this hypothesis in the ECLIPSE (Evaluation of C...