We present an unusual case of cerebellar haemorrhage followed by tension pneumocephalus several days after thoracotomy for resection of a Pancoast tumour. The postoperative course of the 32-year-old patient was complicated by a cerebellar haemorrhage and hydrocephalus caused by compression of the fourth ventricle. Immediate surgical evacuation of the haemorrhage and placement of an external ventricular drain was performed. Respirator ventilation maintaining a continuous positive airway pressure was required. Following weaning and extubation the patient rapidly deteriorated and became comatose. A cranial CT scan revealed a dilated ventricular system filled with air, and air in the subarachnoid space. Recovery of consciousness was observed after aspiration of intracranial air through the ventricular drainage. Recurrent deterioration of consciousness after repeated air aspiration indicated rapid refilling of the ventricles with air. The patient underwent emergency surgical re-exploration of the thoracic resection cavity: dural lacerations of the cervico-thoracic nerve roots C8 and Th1 were identified. Subarachnoid-pleural fistula, cerebellar haemorrhage and tension pneumocephalus after discontinuation of continuous positive airway pressure respiration are unusual complications of thoracic surgery. We discuss the putative pathomechanisms and present a brief review of the literature.