Background: In the pediatric population, acute pharyngo-tonsillitis represents one of the most frequent causes of access to outpatient treatment and use of antibiotics. In frequent tonsillitis, the pharmacological approach is no longer effective, and, therefore, surgery becomes the treatment of choice. Methods: This study compares the prophylactic efficacy of Streptococcus salivarius K12 (Bactoblis®) in children with recurrent pharyngo-tonsillitis treated vs untreated, with a 12 -month follow-up. The primary objectives are: The incidence of recurrence of pharyngo-tonsillar episodes and the concomitant use of other drugs. Secondary objectives are: tolerability of the treatment, the effectiveness in terms of clinical improvement, days of absence from school, reduction of the use of standard therapies, and cancellation from the surgical planning list. Results: Patients belonging to group A (treated with K12 for 90 days) were 24 males and 26 females, mean age 6.6 years (SD=1.57), those belonging to group B (untreated) were 23 males and 27 females, average age 6.8 years (SD=1.72). In the follow-up, group A reported 26 inflammatory pharyngo-tonsillary episodes in the first trimester, unlike group B, who reported 72 in the second trimester. This has shown a lower incidence (3.38%) of the disease compared to group B (6.66%), for a total of 169 inflammatory pharyngo-tonsillary episodes in group A against 333 in group B. A reduction in days of school absence of 429 days in group A and 927 days in the control group (P<0.01) was also noted. Finally, 14 children of group A (28%) underwent adenotonsillectomy, against the whole group B. No adverse events were reported. Conclusion: The efficacy of K12 on the prevention of pharyngo-tonsillar infections, the decrease in the use of antibiotics and the improvement of the overall quality-of-life was confirmed, with a decreased number of absences from school and fewer patients undergoing surgery.