Sinusitis is a frequent complication of respiratory tract infections. Probiotics are perceived to be useful in infections, allergies, and inflammations. Our prospective trial stratified 204 children with recurrent rhinosinusitis by age (2–11 years, 54m:64f; 12–18 years, 39m:47f) and assigned them to standard treatment (antibiotics, anticongestants) or additional 60 days Symbioflor-1 (SF1; Enterococcus faecalis 1.5–4.5x107 CFU). The number of sinusitis episodes was lower in SF1-treated patients (2.52±0.91) than among controls (3.27±1.36; p=0.01). Mean duration of the first sinusitis episode was 11.9±8.6 days with SF1, whereas it was 16.1±12.9 days in the younger controls (p=0.023) and 9.86±5.05 days in the elder controls (n.s.). Duration of subsequent sinusitis episodes was also shorter in SF1 patients (15.2±13.6 days) compared with controls (22.7±14.8 days; p=0.030). No adverse events were observed. Probiotic Enterococcus faecalis adjuvant to conventional therapy can reduce the number and duration of rhinosinusitis episodes in children and adolescents.