To investigate how the extensiveness of a lean implementation-that is, the extent to which lean as a new practice is adopted across nursing departments-relates to second-order problem solving behaviour of nurses.Lean implementation is expected to stimulate nurses' second-order problem-solving behaviour.We used a vignette-based survey to look for differences in second-order problem-solving behaviour in early-adopter and late-adopter departments at two hospitals with differing degrees of extensiveness of lean implementation.At the hospital with an extensive lean implementation, nurses at the early-adopter department showed 71 second-order problem-solving responses from 50 problem scenarios, as compared with 39 responses from 37 scenarios in the late-adopter department. At the hospital with a less extensive lean implementation, these numbers were 16 from 23 compared with 18 from 19.The nurses in the hospital with an extensive lean implementation show more second-order problem-solving behaviour than those in the hospital with a stand-alone approach in a single department.Extensive lean implementation where management clearly shows its belief in lean is a more favourable environment for changing the problem-solving behaviour of nurses.