Postpartum spontaneous pneumomediastinum (Hamman's syndrome) is a very rare event with an estimated incidence of 1 in 100,000 deliveries. It occurs mainly in the second stage of labor and is potentially lethal. We report the case of a 29-year-old primiparous woman during the immediate puerperium (Leff's fourth stage of labor) presenting with acute chest pain, dyspnea and petechiae. She was admitted to the intensive care unit with a suspected diagnosis of amniotic fluid embolism. A chest radiograph revealed a pneumomediastinum that finally resolved with oxygen therapy and supportive management in 3 days.