Background: Despite the importance of identifying and managing a pulmonary exacerbation, and its use as an outcome measure in interventions, there is no standardised definition in cystic fibrosis. In achieving standardised criteria it is important to identify patient-reported indicators. Methods: Interviews were undertaken with 35 school aged children. They reported symptoms experienced during a pulmonary exacerbation in two ways: the first symptoms they become aware of, and how they recognised when they were improving. Interviews were taped, transcribed verbatim and the data analysed thematically. Results: For many children, the onset of an exacerbation was characterised by 'cold' symptoms, tiredness, and changes in cough. For those with moderate or severe disease, sleep disruption, activity induced breathlessness, changes in mood, sputum volume and lack of appetite were common. When describing improvement children focused initially on activities they were now able to perform accompanied by improvements in tiredness and cough. Those with moderate or severe disease also reported improvements in sleep and mood, breathlessness, sputum volume and colour. Conclusions: Child-reported indicators of a pulmonary exacerbation tend to map onto those reported by adults. These results provide the rationale for the development of a single scale for school age children and adults that could be sensitive to progressive stages of CF disease.