Sustainability is one of the most pressing issues of our time and an increasing number of organizations seeks to integrate sustainability into their processes and practices. Research shows that internal sustainability-related communication plays an important role in the process of implementing sustainability in organizations and projects. In spite of that, the role of internal communication in sustainable project management remains a fairly understudied topic. The study aims to address this research gap by exploring the ways in which internal sustainability communication is organized and perceived in the context of sustainable project management. Building on theories of internal communication, sustainability communication and sustainable project management, the following research questions were formulated: In what way is internal sustainability communication organized within a project context? What are project team members’ perceptions of internal sustainability communication? The research is based on a case study of a large infrastructure project in Sweden. Data was collected through semi-structured interviews and document analysis. The study results provide evidence, supported by literature, that how sustainability communication was organized and perceived was counterproductive for the implementation of sustainability within the case study. The results also reveal that project complexity impacts internal communication processes and vice versa. Some practical recommendations are given to tailor sustainability communication to the needs of project team members. Further research on this topic is necessary to develop a more comprehensive understanding of sustainability communication in the context of sustainability projects