Purpose: Lean implementations in hospitals tend to be lengthy or lack the desired results. In addressing the question, how can lean be implemented effectively in a hospital-wide setting, this paper aims to examine two opposing approaches. Design/methodology/approach: The authors studied two Dutch university hospitals which engaged in different lean implementation approaches during the same four-year period: top-down vs bottom-up. Inductive qualitative analyses were made of 49 interviews; numerous documents; field notes; 13 frontline meeting observations; and objective hospital performance data. Longitudinally, the authors depict how the sequential events unfolded in both hospitals. Findings: During the six implementation stages, the roles played by top, middle and frontline managers stood out. While the top managers of one hospital initiated the organization-wide implementation and then delegated it to others, the top managers of the other similar hospital merely tolerated the bottom-up lean activities. Eventually, only the hospital with the top-down approach achieved high organization-wide performance gains, but only in its fourth year after the top managers embraced lean in their own daily work practices and had started to co-create lean themselves. Then, the earlier developed lean infrastructure at the middle- and frontline ranks led to the desired hospital-wide lean implementation results. Originality/value: Change-management insights, including basic tenets of social learning and goal-setting theory, are shown to advance the knowledge of effective lean implementation in hospitals. The authors found lean implementation “best-oiled” through role-modeling by top managers who use a phase-based process and engage in close cross-hierarchical or co-creative collaboration with middle and frontline managerial members.