Asthma is underdiagnosed in France. Asthma can often be diagnosed on the basis of symptoms, help by specific questions useful to consider the diagnosis. Measurement of lung function is important, for diagnosis, evaluation of the reversibility, the variability and the severity of bronchial obstruction. Indeed, patient with asthma may have a poor recognition of their symptoms and a poor perception of bronchial obstruction. Peak expiratory flow meter is an important aid in the diagnosis of asthma but measurements do not always correlate with other measurements of lung function. Allergic status and risk factors must be identified to control environmental exposure.