Objectives- We prospectively analyzed children with acute chest pain and clinical suspicion of pneumothorax (PNX) evaluated at the pediatric Emergency Department. Methods- After clinical examination and before Chest X-Ray, children underwent LUS to evaluate the presence of PNX. We enrolled 70 children, 13 (18,57%) received a final diagnosis of PNX. Results- In all 13 (100%) patients LUS showed the “bar-code sign”, the absence of lung sliding and the absence of B lines while in 12 (92,3%) there was the lung point, giving a diagnosis of PNX. All cases had PNX features on CXR. The “bar-code sign”, the absence of lung sliding and the absence of B lines had a sensitivity of 100% and a specificity of 100%. The “bar-code sign” had a positive predictive value of 100% and a negative predictive value of 100% for the detection of PNX. Conclusions- LUS is highly accurate in detecting or excluding pneumothorax in children with acute chest pain evaluated in the pediatric emergency department.