Purpose: The purpose of this paper is to provide the top ten reasons of process improvement projects termination or failure to Lean and Six Sigma professionals and researchers. Design/methodology/approach: The top ten reasons of process improvement projects termination or failure are based on literature, interaction of authors with Lean Six Sigma Master Black Belts, consultants, practitioners and trainers on various topics of Lean, Six Sigma, general quality management and continuous improvement along several years’ experience of the authors. Findings: The top ten reasons in our opinion include lack of commitment and support from top management; poor communication practices; incompetent team; inadequate training and learning; faulty selection of process improvement methodology and its associated tools/techniques; inappropriate rewards and recognition system/culture; scope creepiness; sub-optimal team size and composition; inconsistent monitoring and control; and resistance to change. Research limitations/implications: The top ten reasons mentioned in this study are based on only literature and authors’ opinion. The authors of this paper have been pursuing a global study to critically evaluate the reasons behind process improvement projects failure based on a case-study approach. Originality/value: The chief operations officers and senior executives of various businesses can use these top ten reasons to develop project failure risk mitigation strategies and save significant cash-savings associated with such project terminations or failures in some other cases. © 2018, Emerald Publishing Limited.