Background: Lung ultrasound (LUS) has been shown to be a useful clinical tool in pediatrics. LUS has been well studied in other respiratory conditions, but very little is known about the LUS findings of asthma. Objectives: The primary objective was to characterize LUS findings of pediatric patients before and after a chemically-induced bronchospasm. The secondary objective was to evaluate the effect of bronchodilators on the LUS findings. Methods: Eligible patients 6 to 17 years old presenting for a methacholine challenge test (MCT) in a pediatric respiratory clinic were recruited. LUS was performed before and after the MCT as well as after bronchodilator administration. LUS were analysed by an expert blinded to the patient characteristics and MCT results. Results: 44 patients were included in the study. 5 patients had positive LUS findings at baseline. 15 patients had a positive LUS following the MCT. There was a significant association between having a chemically-induced bronchospasm and a positive LUS post-MCT (p=0.05, odds ratio 5.3, 95% CI [1.0-27.7]) . Among patients who developed positive LUS findings post-MCT, 4 out of 9 returned to having a negative LUS post-bronchodilator administration. Conclusions: This is the first known report of an association between LUS findings and bronchospasm in pediatric patients. It is also the first documentation of resolution of LUS findings post-bronchodilator administration. Most LUS findings observed were small and limited to one or a few intercostal spaces. Further research is required to evaluate the effect of bronchodilators on LUS in the emergency department.