The efficacy and safety of azithromycin and penicillin V in the treatment of acute streptococcal pharyngitis/tonsillitis in paediatric patients were compared in a double-blind, double-dummy prospective study. A total of 489 children (age range, 2-13 years) were randomized to receive treatment with penicillin V (125-250 mg 4 x daily for 10 days) or azithromycin in an oral suspension (10 or 20 mg/kg 1 x daily for 3 days). Only patients with baseline cultures positive for Streptococcus pyogenes and complete clinical and microbiological assessments at the end of the therapy and follow-up one month later were included in the efficacy analysis. A satisfactory clinical response (cure or improvement) was recorded in 99% of the 10 mg/kg azithromycin group, 100% of the 20 mg/kg azithromycin group, and 97% of the penicillin V group at the end of therapy (day 12-14). At the follow-up evaluation (day 28-30), relapse rates in patients cured or improved at the end of therapy were 6%, 5%, and 2%, respectively. Bacteriological eradication rates at the end of therapy were 98% in both azithromycin groups and 92% in patients who received penicillin V (p = 0.011); pathogen recurrence was recorded at follow-up in 4% of the 20 mg/kg azithromycin group and in 6% of both the 10 mg/kg azithromycin and penicillin V groups. Treatment-related adverse events, the majority of mild to moderate severity, occurred in 13% of patients in the 20 mg/kg azithromycin group, 9% in the 10 mg/kg azithromycin group, and 5% in the penicillin V group. Azithromycin in a dosage of 10 or 20 mg/kg/day one daily for three days was as safe and effective as penicillin V administered four times daily in the treatment of paediatric patients with acute pharyngitis/tonsillitis.