During the last decade, Lean Six Sigma (LSS) in healthcare organizations has increased; however, most cases are registered in developing countries. We aim to show a detailed implementation of Lean Six Sigma in the Emergency Department of an Ecuadorian Children's Hospital to evaluate the applicability of LSS in a South American country and identify barriers, success factors, and tools applied. Following the Define-Measure-Analyze-Improve-Control (DMAIC) methodology, the waiting time in front of the register and treatment section decreased by 79.5% and 53.2%. The total service time was reduced by 55.6%, and the total waiting time decreased by 57%. An external team of experts led the implementation, which resulted in one of the critical success factors. Together with the leadership of the Hospital Director, it helped to reduce the most common barriers found in developing countries, such as lack of training, resistance among the staff, and lack of available data.