Pneumomediastinum is defined as the presence of air in the mediastinum, and may be secondary to trauma or spontaneous. We present the case of a four-year old patient with a spontaneous pneumomediastinum secondary to a violent cough episode, presumably due to a simple cold. The presence of cervical pain, swelling and crepitus warned the pediatrician, who ordered the patient admission. Diagnosis was confirmed by chest and neck plane x-rays. The disorder had a short duration and favorable outcome with no specific treatment aside from symptomatic. CT scan performed at admission revealed an air migration through the perivasculobronchial sheath towards the mediastinum, the so-called "Macklin effect". This is the first description of this entity in pediatrics.