Port congestion is one of the most important factors for measuring port performance and a critical problem that affects seaports' performance, productivity and efficiency levels as well. Determining the most important factors affecting the port congestion in detail contributes to the economic and social growth of the ports. This paper makes an effort to contribute to the existing literature by determining importance weights of factors leading to port congestion as the unique study on the matter. Therefore, it is aimed to identify the most important factors on port congestion according to the port state control, flag state control and independent surveyors' points of views. For this purpose, a literature research was conducted on the factors causing port congestion and experts on the field were consulted. Then the collected data were classified in a list and the determined factors have been ordered with Analytic Hierarchy Process method by experts. The importance weights of the factors have been identified and the most significant factors for port congestion have been obtained with the pairwise comparison of the criteria. According to the results, it can be argued that the most important main factors for port congestion are documentation procedures, port operation and management, ship traffic inputs, port structure and strategy and government relations, respectively.