One of the main problems faced by large retailers is related to the lack of supply in display racks, the so called stock-out points. Studies have been made since the sixties, which show that progress related to this subject is limited. Stock-out levels are around 8.3%. Furthermore, literature on the subject is insufficient, as very few studies have been dedicated to investigating the causes of stock-out. The present study aims to collect stock-out data from a large textile retailer for a product category and elaborate a tree of stock-out causes. Qualitative and quantitative methods were used in this research, through software and interviews, in order to generate and refine our results. From this approach, it was possible to identify that 38% of the causes of stock-outs are within the store, that is, the product is not available in the sales area, but in the back end.