Objectives:To investigate the relationship between lean adoption and problem-solving behaviour in nursing teams, and to explore the practices of lean leaders on nursing wards to reveal how they can stimulate second-order problem-solving within their teams.Design:A mixed-methods retrospective multiple case study using semistructured interviews. Interview data were used to assess the level of lean maturity (based on a customised validated instrument) and the level of second-order problem-solving (based on scenarios). Within-case and cross-case analyses were employed to identify lean leadership practices.Setting:14 nursing teams, with different levels of lean maturity, in a Dutch hospital.Participants:Three members of each nursing team were interviewed: the team leader, one nurse from the ward's core team for the lean-based quality improvement programme and one nurse outside the core team.Interventions:The nursing teams were in various phases of a lean-based quality improvement programme: 'The Productive Ward - Releasing Time to Care'.Results:A strongly significant positive relationship between lean maturity and second-order problem-solving was found: β=0.68, R2=0.46, p<0.001. Further, the results indicated a potential strengthening effect of lean leadership on this relationship. Seven lean leadership practices emerged from the data collected in a nursing ward setting: (1) convincing and setting an example; (2) unlocking individual and team potential; (3) solving problems systematically; (4) enthusing, actively participating and visualising; (5) developing self-managing teams; (6) sensing, as orchestrator, what is needed for change; and (7) listening, sharing information and appreciating. These practices have a strong link with transformational leadership.Conclusions:As lean matures, nursing teams reach a higher level of second-order problem-solving. In later stages, lean leaders increasingly relinquish responsibility by developing self-managing teams.