In today‟s manufacturing environment, different parts manufactured in-house and bought from suppliers are often assembled together into a finished product. Competition has made it very important for companies to deliver a customized product on a promised date. However, when inventory items are missing at the time of production, lead times for products become uncertain and this makes it difficult to fulfill a customer order on the promised date. It is thus important to explore the causes of missing items at the time of production in order to solve such a problem. This Master of Science thesis carried out through a case study at Fläkt Woods in collaboration with Jönköping University is about the problem of not finding specific inventory items in the locations specified by the computer system. It is delimited to inventory items which are physically within the company premises or which according to the computer system are within the premises of the company. The questions at issue have been what the causes of the problem of missing items within the company are and how to effectively reduce the problem. The thesis has been carried out over an entire academic semester as a full-time work in the company. The sources of the problem have been found to be the result of the work procedure, the underlying software used during work (the in-house developed ERP system), stealing from orders, ineffective barcode scans, re-sequencing at the component manufacturing department (called pre-manufacturing in the company) due to the need to fulfill multiple objectives, set-up times at the component manufacturing department and human errors among others. The suggestions given include: modification of the work procedure and the underlying software used at work, increasing effective scanning and using some checks at critical points in the material flow. Areas for further research are given to further reduce the impact of the problem on the production system.