Current COPD guidelines such as the GOLD workshop report use a fixed FEV1/FVC value (0.70) to define airway obstruction, and FEV1 % predicted to classify COPD severity. Evidence is emerging that this approach leads to an unacceptable percentage of false-positive diagnoses of mild and moderate COPD. Expressing FEV1 as a percent predicted value similarly introduces a bias: small people, elderly people, and especially small elderly people who are in good respiratory health will be incorrectly identified as having an abnormally low FEV1. More appropriate classification rules for defining the presence and severity of airway obstruction are urgently needed, especially for primary care doctors who have to deal with the early stages of COPD. The use of the lower limit of normal (LLN) for the FEV1/FVC ratio instead of a fixed ratio value of 0.70 would be a first rational step towards a better classification of airway obstruction.