ObjectiveTo assess the value of performing routine pulmonary function tests by flow‐loop spirometry in young adolescents with asthma. DesignA prospective clinical study comparing clinical assessment and patients' self‐reporting of asthma severity with the results of pulmonary function tests. SettingGeneral practice in a small rural community of about 30000 people. PatientsYoung adolescents with asthma, aged 10‐15 years, were enrolled in the study over a two‐year period from July 1993 to June 1995 when they presented for either elective, interval assessments or with an acute exacerbation of asthma. Main outcome measuresDiscrepancy between (i) the doctor's and the patient's perception of asthma control (six scale measures) and the consequent management plans, and (ii) the results of pulmonary function tests that indicated less than adequate airway function (i.e., forced expiratory volume in one second as a percentage of predicted vital capacity for height and sex [FEVi%] less than 65% or average flow rate over the middle 50% of forced vital capacity as a percentage of predicted normal value [FEF25%‐75%] less than 65%). ResultsTwenty‐seven adolescents with asthma were assessed on a total of 37 occasions. The results of pulmonary function tests did not correlate with asthma symptoms and treatment in 11 of the 37 assessments (30%; 95% confidence interval [Cl], 16%—47%). The 11 assessments were performed on eight patients. ConclusionsThis small community‐based study of adolescents with asthma supports the view that pulmonary function testing by flow‐loop spirometry should be part of the routine assessment of acute and chronic asthmatics. Further study in a larger community is needed to clarify the frequency of over‐ and underestimation of asthma severity in this difficult age group.