Purpose This paper aims to expand the knowledge about Lean Six Sigma (LSS) implementation in the public sector. By analyzing an LSS improvement initiative in a German municipality, examples of success, barriers and challenges are discussed. A comparison with literature regarding the production and service sectors unfolds similarities and differences. Design/methodology/approach The paper applies the action research method. Especially for the broad field of project management, methods focusing on actual experience from practice have been recommended by many researchers. Findings Implementations of LSS in the public sector seem to be particularly challenging and lengthy. Change and communication management have proved to be the most important aspects to successful acceptance, cooperation and improvement sustainability. In the analyzed cases, the needed volume of data could often not be procured. The applied Six Sigma methodology primarily included the DMAIC project phases as well as selected standard instruments. In contrast, the lean elements of LSS achieved more results and were appreciated by project team members. Originality/value The LSS application in this paper provides insights into practical implementation experience in a municipality, as well as lessons learned. Until now, most research addressed the single application of lean, continuous improvement or Six Sigma. This paper represents the first academic report of a LSS program in a German municipality and underlines the need for scientific support of those initiatives in further municipalities worldwide.