Many organisations are implementing 'lean manufacturing' (LM) with the objective of achieving a superior competitive advantage over other organisations. Few companies have attained their objective, while many of them did not. One of the reasons for failure is that the managers of these organisations have not understood clearly: how the performance measures of an organisation are affected, when it gets transformed through LM. This paper is an attempt to fill in this gap. It reviews the literature related to LM, simulation and explores how simulation can be used along with value stream mapping (VSM). It describes a case of a shop floor of an automobile industry, where LM is getting implemented and demonstrates the application of QUEST simulation software for developing the simulation models for both current and future state VSMs. These models will help the managers to analyse the impact of various LM elements on the performance measures of the organisation. Copyright © 2009, Inderscience Publishers.