In a series of 497 PDT procedures done in the intensive therapy unit at Morriston Hospital between 1992 and 1999, PDT was abandoned because of bleeding in 6 patients and was noted to be a problem in a further 18 cases (overall incidence 4.8%). In all cases, haemorrhage was successfully arrested. Surgical tracheostomy was necessary in 6 of these 24 cases. The source of bleeding in 4 of these patients was attributed to the inferior thyroid vein (2 cases), high brachiocephalic vein, and possibly an aberrant anterior jugular communicating vein, respectively. In one patient, the vessel presumed injured could not be identified and in another patient, bleeding was related to multi-system disease. We conclude that the risk of bleeding, although low, can be minimised if the operator maintains a high index of suspicion for aberrant vascular anatomy and investigates possible abnormalities with diagnostic ultrasound. Injury to vessels low in the neck can be reduced by not fully extending the neck and siting the stoma at the upper tracheal rings. The possibility of developing a tracheoarterial fistula is reduced if the stoma is situated above the 4th tracheal ring and fibreoptic endoscopy is used to confirm correct tracheostomy tube placement.