Chronic obstructive pulmonary disease (COPD) exacerbation frequency is important for clinical risk assessment and trial recruitment. In order to accurately establish exacerbation frequency, patients need to be followed for 1 yr, although this is not always practical. 1) Patient recall of exacerbation number during the year prior to recruitment to the London COPD cohort was compared with the number of exacerbations recorded on diary cards during the subsequent year; and 2) patient recall of their exacerbation number after 1 yr of follow-up was compared with documented exacerbations over the same year. A total of 267 patients (forced expiratory volume in 1 s 1.14 L) recorded worsening of respiratory symptoms on daily diary cards for 1 yr. Exacerbations were defined according to previously validated criteria. There was no difference between the exacerbation number recalled by patients prior to recruitment and the number detected during the first year (median 2.0 (interquartile range 1.0-4.0) and 2.0 (1.0-4.0); expected agreement 76.4%; agreement 84.6%; κ = 0.3469). There was no difference between the number of exacerbations remembered by patients and the number recorded on diary cards over the same 1-yr period (2.0 (1.0-4.0) for both groups; expected agreement 74.9%; actual agreement 93.3%; κ = 0.6146). Patients remember the number of exacerbations they have in a year. Accuracy is increased when comparing the same 1-yr period. Patient recall is sufficiently robust for stratification into frequent and infrequent exacerbator groups for subsequent years.