Background: Albeit not recommended because of contradictory results, nebulized 3% hypertonic saline is widely used for treating acute viral bronchiolitis. Whether clinical differences may be attributed to the type of nebulizer used has never been studied. Objectives: By modifying the amount of salt deposited into the airways, the nebulizer characteristics might influence clinical response. Methods: A prospective, randomized, controlled trial included infants hospitalized in a French university hospital for a first episode of bronchiolitis. Each child received 6 nebulizations of 3% hypertonic saline during 48 h delivered with 1 of the 3 following nebulizers: 2 jet nebulizers delivering large or small particles, with a low aerosol output, and 1 mesh nebulizer delivering small particles, with a high aerosol output. The primary endpoint was the difference in the Wang score at 48 h. Results: Only 61 children of 168 were recruited before stopping this study because of severe adverse events (n = 4) or parental requests for discontinuation due to discomfort to their child during nebulization (n = 2). One minor adverse event was noted in 91.8% (n = 56/61) of children. A high aerosol output induced 75% of the severe adverse events; it was significantly associated with the nebulization-induced cough between 24 and 48 h (p = 0.036). Decreases in Wang scores were not significantly different between the groups at 48 h, 9 recoveries out of 10 being obtained with small particles. Conclusion: No beneficial effects and possibly severe adverse events are observed with 3% hypertonic saline in the treatment of bronchiolitis.