Tens of thousands of patients undergo haematopoietic stem-cell transplantation (HSCT) annually, primarily for haematological and lymphoid cancers, but also for other disorders. 1 Intensive care support is provided for 15–40 per cent of HSCT recipients, most of whom require mechanical ventilation for respiratory failure. 2 Although recent studies have shown improvement in outcome, the mortality rate of HSCT recipients receiving invasive ventilation may exceed 90 per cent. This chapter describes the pulmonary complications that develop in HSCT recipients.