To compare the long-term effects of different postoperative treatment regimes after functional endoscopic sinus surgery (FESS), we performed a randomized controlled trial. Inclusion criteria were chronic rhinosinusitis with (CRSwNP) or without (CRS-NP) bilateral nasal polyps and acute recurrent rhinosinusitis (ARR). All patients (male/female = 56/65; mean age = 42.8 years; age range 18-73 years) underwent sinus surgery for the first time. The patients included in 2004 were allocated to a packing in middle meatus for 5 days or saline irrigation only postoperatively. The patients included in 2005 were randomized to debridement 6 and 12 days postoperatively or saline irrigation. At baseline and 56 weeks (32-77) postoperatively, the patients reported symptoms such as nasal congestion, facial pain, headache, and change in sense of smell, nasal discharge, sneezing and reduced general condition on visual analogue scale (VAS). We used ANCOVA to compare symptom improvement. Among patients with CRSwNP, nasal congestion and sneezing improved, respectively, 20 mm (P value = 0.041) and 18 mm (P value = 0.011) more in the debridement group than in the saline irrigation group. Although a packing had positive effects on the symptom improvement they were not significant. Patients with CRSwNP, who had undergone debridement after FESS, had significantly larger symptom improvement 56 weeks after surgery than patients who had only done saline irrigation.