Only five cases of subarachnoid-pleural fistula in children have been reported previously. All had a history of trauma and associated neurologic deficit which gave clue to the diagnosis. The authors present a child who presented with a massive, rapidly filling, clear pleural effusion in whom there was no neurologic deficit. The history of an automobile accident in the past had almost been forgotten. A subarachnoid-pleural fistula was discovered on exploratory thoracotomy. The entity should be thought of, and actively investigated, in a child with a history of trauma and a pleural effusion of obscure etiology, even if there is no associated neurologic deficit.