Measuring nasal nitric oxide (nNO) is increasingly used as part of testing for primary ciliary dyskinesia (PCD). The diagnosis of PCD is often delayed until after bronchiectasis is established and auditory damage has occurred. It is important that all paediatricians are aware of clinical features that are suggestive of PCD that should prompt diagnostic testing. nNO levels are recognised to be low in people with PCD and results generated by static chemiluminescence analysers using velum closure technique in older children have good sensitivity and specificity. However, to conclusively rule PCD in or out, further tests of ciliary function are required and assessment of cilia ultrastructure, immunohistochemistry studies and genotyping may also be indicated. These tests are more complex, invasive and expensive than nNO. nNO is less well studied in younger children where tidal breathing measurements are required. Portable nitric oxide analysers are also increasingly used in practice. This paper discusses when to consider PCD as a possible diagnosis in a child along with the indications, physiological and technical background and clinical utility of nNO as a test for PCD in children.