Purpose: The aim of this study is to investigate the outcomes of a leading Swedish truck maker (referred to as “TruckCo” for confidentiality reasons) providing lean training to its strategic suppliers. Design/methodology/approach: A single in-depth case study is conducted, using on-site semi-structured interviews with representatives from TruckCo and its suppliers for data collection. Findings: The lean training program resulted in four main outcomes. First, financially unstable suppliers were less receptive to the lean training program than financially stable suppliers. Second, the suppliers became easier to collaborate with over time, through improving their internal ways of working and thus creating more trust in terms of reliability. Third, the suppliers improved their ability to identify possible problems that could jeopardize deliveries. Fourth and finally, the suppliers improved their delivery precision. Research limitations/implications: One limitation of this study is that its findings are based on a single in-depth case study. Another limitation is that all the involved companies originate from Sweden. These limitations should be considered in attempts to replicate or further test the reported findings. Practical implications: This study provides insights into how a manufacturer can teach lean management to suppliers, and how suppliers can be involved in a manufacturer's journey towards a leaner supply chain. Furthermore, the study reflects more generally on the potential outcomes of a manufacturer providing lean training to suppliers. Originality/value: This study highlights both TruckCo's and the suppliers' view of the outcomes of the lean training program and discusses how different suppliers adopt the taught lean practices. Avenues for future research are proposed as well.