Reported presence or absence of night cough was compared with tape recorded cough in 15 children with perennial asthma (median age, 9 years; range, 7-14) who reported troublesome nocturnal symptoms. Measurements were made and diaries kept for 7 consecutive nights. Cough was reported on 66 of 105 (66%) and recorded on 93 (90%) available nights with poor overall agreement (Cohen's coefficient of assessment, kappa +0.30, range -0.17 to +1). The poor agreement between subjective and objective assessment of an important symptom of nocturnal asthma raises questions on the validity of symptom reporting and may in part explain the not infrequent disagreement between medical and patient assessment of disease severity.