Purpose – The purpose of this study is to investigate how companies in third-party logistics operate within customized warehouse solutions to identify which factors affect the work processes.  Method – To fulfil the purpose of the study, a literature study was conducted to create a theoretical framework to obtain an understanding of the subject TPL. Furthermore, to fulfil the purpose, a case study was conducted at a TPL company. The case study consisted of interviews and observations in which generated the empirical data for the analysis. The outcome of the data was interpreted and analysed by triangulation in order to detect patterns from different perspectives.  Findings – It can be stated that the work conducted in TPL-companies with customized warehousing solutions varies, due to the fact that different customers, with different products are handled in different ways. Furthermore, it emerged that there are at least 11 factors, both external and internal, that are estimated to have a direct impact on the work process in TPL- companies with customized warehousing solutions.  Implications – The results of the study have contributed to increasing the understanding of how TPL-companies work with customized warehousing solutions and also contributed to identify a number of factors that affect the work processes. With the result obtained, the study has contributed to supplementing the lack of research concerning TPL from a TPL perspective.  By visualizing the work process in TPL companies with customized warehouse solutions and highlighting factors that affect the work process in customized warehouses, this study can contribute to support the internal work in TPL companies. Furthermore, the improvement measures presented for seven of the factors can be used as a tool for TPL companies.  Limitations – The limitations of the study are that only one TPL company was included in the case study and three of the case company’s employees participated in the empirical collection. If multiple TPL companies and respondents with different areas of responsibility, one could assume that more factors than the 11 found in this study, could have been identified. Thus, the generalizability is limited for the study.