The authors reviewed a series of 553 consecutive patients who underwent endoscopically guided sinus surgery. Major complications occurred in six patients (2.2%). There was one death due to incorrect positioning of the frontal drain. One patient developed a cerebrospinal fluid leak which had to be closed with an osteomucosal graft. Two patients who developed severe bleeding after removal of the nasal packing, needed ligation of the sphenopalatine artery and the internal maxillary artery, respectively. Two patients developed a complete stenosis of the nasolacrimal duct, necessitating a dacryocystorhinostomy. Minor complications occurred in 36 patients (13.4%). These included damage to the lamina papyracea (n = 11), severe bleeding after removal of the nasal packing treated conservatively (n = 6), intranasal mucosal adhesions (n = 17), and atrophic rhinitis (n = 2). The aetiology, prevention and treatment of complications during and after sinus surgery are also discussed.