This is a case report of spontaneous pneumomediastinum that occurred in a 19-year-old army trainee during his 2.4km run. Spontaneous pneumomediastinum is a rare disorder. It is usually precipitated by activities related to Valsalva manoeuvres such as strenuous physical activities, retching and vomiting. Treatment is expectant and the disorder usually resolves spontaneously within a few days. However, one must be aware of the disorder so that additional advice such as avoiding activities that involve Valsalva manoeuvres can be given.