A case of right diaphragmatic eventration, associated with a lung sequestration, in a 7-month-old infant is presented. Failure to thrive was the initial symptom. X-ray of the chest, made because of mild respiratory distress, revealed an inhomogeneous opacification of the right lower hemithorax, suggesting a diaphragmatic hernia. A right thoracotomy was performed and a diaphragmatic eventration covered by a thick pleuroperitoneal membrane was found, together with sequestration of the lung. The pathologic findings and the embryology are discussed.