BACKGROUND: Endoscopic sinus surgery (ESS) produces a great range of potential complications. Rough segregation into "minor" and "major" complications seems insufficient. This study uses a recently published new classification system that is based more on the patient's point of view, with a greater variety of options. METHODS: A retrospective review was undertaken of 421 ESS procedures. Both, the surgeon's experience and the extent of surgery were correlated with the complication rate. RESULTS: The overall complication rate was 39.7% (grades A-D) and did not correlate significantly with either the experience of the surgeon or with the extent of surgery. CONCLUSION: The new classification is simple, precise, and takes complications into account that used to be neglected. ESS is even safe in the hands of less skilled surgeons as long as the degree of difficulty stays highly adapted to his/her ability. Some complications (grade A) seem to be inherent to the procedure.