Seaports are major transport hubs of the global economy. Their activities pose negative impacts on the environment, the social, and the economic dimensions of sustainability. Seaports are complex systems with unique characteristics and their sustainability efforts are dependent on the local context, ownership structure, size, and operations. A number of ports have started to assess and report their sustainability efforts; however, there is limited information on the coverage of sustainability issues and the performance of port sustainability activities. This paper assesses the indicator coverage of 24 sustainability reports of seaports from worldwide that follow the GRI guidelines using the Holistic Assessment of Sustainability Performance in Seaports (HASPS) framework. The HASPS was developed by the authors based on a literature review and expands the GRI guidelines with port-specific indicators and interlinking issues. The results show that there is a great variety of coverage of information disclosed regarding all five dimensions of the HASPS (economic, environmental, social, port system, and interlinking issues). Ports that use the GRI guidelines, management systems and certifications, have a good coverage of sustainability issues; coverage however is better in ports that have developed additional port-specific indicators. The paper highlights the importance of a harmonised port sustainability assessment, which can be used by all ports regardless of their unique characteristics.