Forty adult patients diagnosed with chronic rhinosinusitis who underwent functional endoscopic sinus surgery (FESS), were analyzed with respect to postoperative resonatory voice changes. For evaluation the patients were asked about their subjective impression of voice changes using a questionnaire. An objective assessment was performed by determining the so-called nasalance using the Nasometer (Kay Elemetrics), preoperatively, on the immediate postoperative follow-up (2 days after surgery), and approximately 1 month after surgery. The mean nasalance values increased significantly one month after FESS whereas the immediate postoperative control (2 days after surgery) showed a decrease of nasalance. Although FESS is a minimally invasive procedure, it can change the acoustic characteristics of the vocal tract in the long term and produce a significant increase in nasality. The authors strongly recommend that clinicians inform all patients, in particular voice professionals, about the possible effects of endonasal sinus surgery on voice quality.