The accumulation of chyle into the mediastinum after surgical intervention is considered an extremely rare event, which has been previously described only in adulthood. We report on a 9-month-old boy who developed a cervicomediastinal chyloma after excision of a large left-sided supraclavicular cystic hygroma. Notwithstanding considerable tracheal deviation, the infant remained asymptomatic and was successfully treated by nonoperative treatment. Professionals should be aware of such an unusual condition, which may benefit from expectant management when evaluation establishes a high likelihood of clinical diagnosis, and patient's general condition remains stable. This approach may avoid, with little risk, unnecessary early surgical intervention in some of these patients.