Abstract: The main purpose of this article is to identify the main characteristics of Lean Six Sigma projects executed by efficient companies. To do so, this article explores a large empirical database, with 112,421 projects, executed from 2001 to 2018 in 57 strategic business units from a heavy machinery producer, which is recognised as a worldwide reference in the use of Lean Six Sigma methodology. The research was conducted in two stages, first, the data was analysed with a Network Data Envelopment Analysis (DEA) model, which provided an efficiency ranking formed by the strategic business units. In the second stage, a Classification Tree (CHAID) method was used to identify the common characteristics of the projects accomplished by the most efficient ones. The findings show that these strategic business units are characterised by projects executed in departments closely related to senior management, especially Corporate Governance and Business Strategy. In addition, their projects usually focus on people, innovation, or cost reduction and are structured more frequently with the DMAIC cycle. These findings broaden the understanding of the criteria that should be considered in Lean Six Sigma project selection and prioritisation, by providing new insights (not identified in previous studies) to decision-makers and researchers, from projects associated with the efficient performance of Lean Six Sigma, which can be particularly valuable considering the multiple projects conducted in this initiative, that frequently compete for resources Ver menos