Introduction: Preschool wheeze is a public health issue, due to its high frequency and morbidity. When the disease is severe and uncontrolled, despite optimal treatment, explorations are needed. Patients and methods: We conducted a retrospective study at our tertiary asthma center in Rouen University Hospital, France. Each child under 3 years with severe uncontrolled preschool wheeze was admitted to a pediatric day hospital for a bronchoscopy. We collected the results of clinical, biological and radiological exams, and followed-up data at 1, 2 and 3 years (Y ₊₁, Y ₊₂, Y ₊₃ respectively), to study the evolution of the disease, and identify factors of uncontrolled disease. Results: We included 135 patients; 63 (47%) were still followed-up in our center at Y ₊₃. Median age at inclusion was 12 months. Thirty percent of patients still had severe uncontrolled wheeze at Y ₊₃. Treatments were significantly decreased at Y ₊₃ (p<0.001). A total IgE level higher than 7 kU/L was a factor in uncontrolled wheeze at Y ₊₁, tobacco exposure (p<0.001) and female gender (p=0.05) were factors associated to the persistence of uncontrolled wheeze at Y ₊₂, and a first case of bronchiolitis before 2 months old was a factor in uncontrolled disease at Y ₊₃ (p=0.007). Discussion: Our study is unique in terms of its very young population, with very severe wheeze (80% of children included with a history of hospitalization, 8% in intensive care). Our therapeutic approach is original, enabling us to study the evolution of “therapeutic pressure” in the early years of this frequent disease, the pathophysiology of which is still poorly understood.