Customized clothing manufacturing is a clothing manufacturing method realized and performed in a collaboration between the manufacturer and the customer. In this manufacturing method, the customer is offered a basic piece of clothing and various options (fabric, model, color, style, accessories, printing on clothing, etc.) so that the customer can modify the clothing and design the most suitable garment for him or her. Thanks to this manufacturing method, the customer has the opportunity to purchase the most appropriate personalized clothing while, at the same time, the manufacturer achieves a high profit margin by making a customized product. Customized clothing production is an important method in the industry because it increases both the profit margin of the enterprises and the level of customer satisfaction. Although it is not yet a very common method, it is expected that it will become widespread in the future with technological developments. Within the framework of this study, we focused on online customized t-shirt manufacturing. The study was carried out in three stages. In the first stage, the design options that young consumers prefer and/or need for online customized t-shirt design were determined. In the second stage, websites that perform the manufacturing of customized t-shirt that are available online in Turkey were determined. In the third stage, online t-shirt design options determined in the first stage were presented to the customers by the websites determined during the second stage. According to the assessment, customized t-shirt design websites active in Turkey were found to be adequate in terms of the “design with respect to body sizes” option whereas the websites were found partially adequate in terms of other options. In addition, some design options that online personalized t-shirt design websites intend to offer change according to the gender and education of young consumers.