The place of systemic corticosteroids in the treatment of children with chronic rhinosinusitis (CRS) remains unclear. We aimed to assess the effectiveness and tolerability of oral methylprednisolone (MP) as an anti-inflammatory adjunct in the treatment of CRS in children.Forty-eight children (age 6-17 years) with clinically and radiologically proven CRS were included. Patients were randomly assigned to either oral amoxicillin/clavulanate (AMX/C) and MP or AMX/C and placebo (P) twice daily for 30 days. Oral MP was administered for the first 15 days with a tapering schedule. Primary parameters were mean change in symptom and sinus computed tomography (CT) scan scores after treatment. Secondary study parameters were mean changes in individual symptom scores after treatment, relapse rate and tolerability. Forty-five patients completed the study, 22 received AMX/C and MP, and 23 AMX/C and P. Both groups demonstrated significant improvements in symptom and sinus CT scores, comparing baseline to end of the treatment (p<0.001). Methylprednisolone as an adjunct was significantly more effective than placebo in reducing CT scores (p=0.004), total rhinosinusitis symptoms (p=0.001) and individual symptoms of nasal obstruction (p=0.001), postnasal discharge (p=0.007), and cough (p=0.009). At the end of the treatment, 48% of the children in the P group still had abnormal findings in CT versus 14% in the MP group (p = 0.013). Therapy-related adverse events were not different between groups. Although insignificant, the incidence of clinical relapses was also less in the MP group (25%) compared to P group (43%) (p = 0.137). Oral MP is well tolerated and provides added benefit to treatment with antibiotics for children with CRS.