Lean Six Sigma (LSS) is a common methodology adopted by organizations to improve operational and financial performance by removing waste and reducing variation. While literature agrees LSS is beneficial, it is unclear whether the initial improved performance is sustained over time. Research has identified several critical success (CSFs) and failure (CFF’s) factors which determine the effectiveness of LSS implementation along with its sustainability. Integral in sustaining the initial positive impact is recognizing these success factors during LSS implementation in conjunction with identifying and preventing critical failure factors.This study aims to investigate whether the implementation of LSS has sustained a positive impact on the operational and financial performance of a Medical Device Company based in the West of Ireland. Using a mixed method approach; a case-study within one Medical Device organization was conducted. Key performance indicators (KPI’s) such as defects and non-conformances were analyzed and trended. Additionally, survey data of critical success and failure factors in the areas of management, training, and culture was collated. The quantity of unit rejects, which ultimately leads to increased costs was used as the financial indicator in this study. The influence of Quality 4.0 and the global pandemic were also considered. A comparison was then made with two other similar sized companies in the region using semi- structured interviews.Results indicated LSS has a sustained positive impact on the organization’s operational and financial performance. Findings suggest Quality 4.0 was a significant contributing factor for sustaining this positive performance. The pandemic was shown to magnify the failure factors albeit offset somewhat by Quality 4.0. The comparison with the other two medical device organizations suggested that LSS alone could not sustain a positive impact highlighting the need to conduct further research into self-sustaining LSS methodologies along with the value to consider the new ‘LSS 4.0’ approach.