Résumé : Background: Persistent low membership is observed in many community-based health insurance (CBHI) schemesin Africa. Causes for low membership have been identified and solutions suggested, but this did not result inincreased membership. In this case study of the mutual health organisation of Dar Naïm in Mauritania we explorethe underlying drivers that may explain why membership continued to stagnate although several plans for changehad been designed.Methods: We used a systems approach focussed on processes, underlying dynamics and complex interactions thatproduce the outcomes, to delve into 10 years of data collected between 2003 and 2012. We used qualitativeresearch methods to analyse the data and interpret patterns.Results: Direct causes of stagnation and possible solutions had been identified in the early years of operations, butmost of the possible solutions were not implemented. A combination of reasons explains why consecutive actionplans were not put into practice, showing the complexity of implementation and the considerable managementcapacity required, as well as the challenges of integrating a novel organisational structure into exiting socialstructures.Conclusions: For any CBHI project aiming at high membership, skilled professional management seems essential,with capacity to question and adapt routine procedures and interpret interactions within the wider society.Countries that include community-based health insurance in their strategic plan towards universal coverage willhave to pay more attention to management capacity and the minutiae of implementation.