We have undertaken an observational retrospective cohort study to assess feasibility and clinical effectiveness of early rehabilitation in patients recovering from acute exacerbation of COPD (AECOPD). A cohort of 1826 inpatients (73% male, age 70+/-8 yrs, FEV(1) 50+/-16% pred.) admitted to a pulmonary rehabilitation (PR) program and completing at least 15 sessions were divided into categories according to their dyspnoea grade (Medical Research Council--MRC scores 2-5) as assessed before AECOPD. The pre-post changes in 6-minute walking distance (6MWD) test, perceived end-effort dyspnoea (Borg scale), and self-reported quality of life (St. George's respiratory Questionnaire: SGRQ) were measured throughout. Absolute change in 6MWD (52 [95%CI 45-59], 65 [95%CI 60-70], 63 [95%CI 59-66], and 70 [95%CI 67-74] meters in MRC 2-5 respectively) and the percentage of patients achieving the minimal clinically important difference (MCID) of +54 m (40, 55, 57, and 61%, respectively, p=0.001) differed across MRC grades. Proportion of patients able to reach > or = 350 m at the 6MWD after PR was higher in MRC 4 and 5 (18 and 22%) as compared to MRC 2 and 3 (6 and 15%). Early PR in a cohort of AECOPD patients is feasible and it is associated to clinically meaningful improvement in exercise tolerance independent on the severity of dyspnoea. The proportion of patients reaching the limit of > or = 350 m after this intervention is higher in the most severe patients.