Although the Lean Management System has helped healthcare facilities improve their bottom-line performance, many remain transitional and have not yet fully transformed into Lean organisations. In order to provide workable ways to counteract these typical trends, this mixed method study investigates the sustainability challenges undermining Lean healthcare to decipher what is restraining South African healthcare institutions from fostering, sustaining and spreading Lean. The study involved a survey of 620 clinicians and 20 key informant interviews - with Lean champions, clinical operations managers and Lean experts involved in Lean initiation in South African hospitals. As indicated in the quantitative findings, the participants' rating of significant obstacles to healthcare quality improvement shows that resource and budget constraints and supply chain inefficiencies are the most predominant challenges. Further, healthcare institutions' management must adopt a strategic approach to Lean; the challenges of leadership style and commitment, staff shortages, information technology resources, and supply chain inefficiencies must be mitigated to make Lean sustainable. The study offers practical solutions to improve the traditional trends.