The complications of the Caldwell-Luc operation were retrospectively studied in 1990. The case records were analysed and updated information from telephone interviews and posted questionnaires were available for most patients. One hundred and eighty-five patients with 216 procedures with a mean postoperative follow-up period of 33.5 months were studied. The commonest indication for the operation was for chronic sinusitis. There were three common complications found: facial swelling (61.9%), pain and/or numbness of the face (46.0%) and pain and/or numbness of the teeth/gums (30.9%). Rare complications are postoperative epistaxis (0.4%), oroantral fistulae (0.4%), epiphora (0.4%) and dental discoloration (0.4%). This paper discusses the pathophysiology of these complications and surgical techniques on how to avoid them. Although the use of the Caldwell-Luc operation has declined in recent years with the development of endoscopic sinus surgery, it still has occasional indications and a set of practical guidelines on how to prevent complications would be useful. The basis for treating chronic sinusitis with functional endoscopic sinus surgery at the expense of the more traditional form of treatment is also discussed.