Asthma is the most common chronic respiratory condition affecting children in the UK. There is no single gold standard test to confirm the diagnosis and both overdiagnosis and underdiagnosis are common. Asthma should be suspected in any child presenting with episodes of wheeze, especially recurrent episodes of wheeze. Clinical diagnosis alone often results in misdiagnosis; all children from the age of five years under investigation for asthma in primary care should have access to spirometry, bronchodilator reversibility and FeNO testing.