Objectives: To evaluate the effects of two different levels of positive end-expiratory pressure (PEEP) during helmet continuous positive airway pressure (HCPAP) support on the intubation rate in infants with bronchiolitis admitted to pediatric intensive care units (PICUs). Design: Multicentric prospective, randomized, open clinical trial. Setting: Four tertiary PICUs in Italy. Participants: Infants admitted to PICUs due to severe bronchiolitis and requiring respiratory support. Interventions: The enrolled patients were randomly assigned one of two PEEP levels for HCPAP support: high (P10 group: 10 cmH ₂O) or low (P5 group: 5 cmH ₂O). Measurements and Main Results: In total, 64 patients were randomly assigned to the P10 group, and 60 to the P5 group. The intubation rate was 9/60 (15%) and 9/64 (14%) in P5 and P10 groups (OR 0.94, 95% CI 0.36-2.46, p=0.99). Of the patients in the P5 group, 47 (78%) were escalated to a PEEP level of 10 cmH ₂O. PEEP level was not associated to intubation rate (OR 0.69, 95% CI 0.19 to 2.40, p=0.57), after adjustment for age, gestational age, high flow nasal cannula application, bronchiolitis severity score and pediatric index of mortality 3. No cases of pneumothorax were observed in this study. Conclusions: In this trial on infants with severe bronchiolitis, a PEEP level of 10 cm H ₂O during HCPAP in comparison to an initial level of 5 cm H ₂O did not show to prevent intubation. These results are not conclusive due to the premature stopping.