In this paper we provide an exploration and analysis of Lean Six Sigma (LSS) implementation in Dutch manufacturing/engineering small- and medium-sized enterprises (SMEs). Critical success factors (CSFs) and impeding factors are identified and analysed. Exploratory empirical evidence about LSS implementation in Dutch SMEs was collected from a survey study on Dutch SMEs. Statistical testing was applied to validate the ranking of the CSFs. To deepen insight in how organizations translate CSFs into practice and cope with impeding factors, additional in-depth qualitative information was gathered from six case studies. Linking to customer, vision and plan statement, communication and management involvement and participation are the highest ranked CSFs. Internal resistance, the availability of resources, changing business focus and lack of leadership are the strongest impeding factors. The case studies confirmed the importance of the CSFs and revealed three new CSFs: personal LSS-experience of Top management, development of the project leader's soft skills and supply chain focus. SMEs in the Netherlands make no distinct separation between lean manufacturing and Six Sigma, but rather apply both approaches intertwined. Journal of the Operational Research Society (2012) 63, 339-353. doi:10.1057/jors.2011.47 Published online 18 May 2011