What is a clean restaurant in customers' viewpoints? Restaurant cleanliness is considered one of the most significant conditions when customers evaluate overall restaurant quality or decide their levels of satisfaction. However, there have been few studies of perceptions of restaurant cleanliness in customers' eyes. Previous studies were found to use inconsistent concepts of restaurant cleanliness when evaluating restaurant cleanliness. For example, some measurement scale of restaurant quality or customer satisfaction includes only items related to a restaurant's interior appearance to measure the restaurant cleanliness. Some researchers have also included items related to server's appearance. In other studies, overall images of a restaurant were used to evaluate its cleanliness. This study attempts to investigate the customers' perceptions of restaurant cleanliness. Understanding what customers consider when they evaluate a restaurant's cleanliness can be beneficial for hospitality managers who can use the information to increase their restaurant's quality and to satisfy their customers. In addition, this study was conducted with two different cultural groups of customers: Westerners and Asians. Understanding how different cultures perceive restaurant cleanliness can help hospitality managers who plan to expand their business in the global market. The results of this study indicated that the items of restroom personal hygiene, restroom appearance and server behavior all have a positive relationship with customers' restaurant quality evaluations. The level of importance of restaurant cleanliness dimensions was found to be similar between the Western and Asian samples. The server's behavior, restroom appearance and signage were found to be the most important dimensions for both groups. However, restroom personal hygiene was found to be the only dimension ranked differently by the two groups in the study. Westerners weighed the restroom personal hygiene as more important than did Asian respondents. Asian groups were found to have higher expectations for overall restaurant cleanliness dimensions than Western groups. / Master of Science