Background:The purpose of this study was to compare the effects of nasal saline irrigation (large volume, positive pressure isotonic saline) in addition to standard treatment in patients with acute rhinosinusitis (ARS). Methods: This parallel, randomized controlled trial was conducted at a tertiary hospital. The adult patients with ARS (age ≥18 years) were randomly assigned to two groups. The irrigation group received 0.9% saline irrigation twice daily, using a 250-ml squeeze bottle, in addition to standard treatment. The no-irrigation group received standard treatment only. Patients were evaluated at baseline, 1 week, and 2 weeks. The quality of life, rhinologic subscore, symptom score, endoscopy score, and cure rate were compared. Results: Sixty-one patients (30: irrigation, 31: no-irrigation) were enrolled. There were 17 males and 44 females. The mean age was 41.06 years. Although both groups showed improvements, the improvement of each outcome was not different between the groups. Subgroup analysis by ARS subtype showed benefits of irrigation in the common cold subgroup; the improvements that were greater than control included: rhinologic subscore, intergroup mean difference −4.15 [95% confidence interval (CI), −7.49, −0.80] at 1 week and −5.23 [95% CI, −9.69, −0.78] at 2 weeks; combined symptom score −5.35 [95% CI, −10.55, −0.14] at 1 week and −8.02 [95%CI, −14.36, −1.70] at 2 weeks. Conclusion:The add-on isotonic nasal saline irrigation using a large volume, positive pressure device did not add benefits equally for all ARS patients. The benefits of irrigation on quality of life and nasal symptoms were only observed in the common cold patient subgroup.