In this case study, we investigate knowledge sharing between virtual volunteers, i.e. volunteers who work remotely by telephone or chat, in a specific non-profit organisation running a helpline. Previous research suggests that knowledge sharing may increase efficiency and continuity in organisations. This can be a challenge for organisations with limited fundings. Also, knowledge sharing between virtual volunteers is an understudied topic. We therefore strive to fill this knowledge gap by exploring how knowledge is shared between virtual volunteers in the selected organisation, and which factors are of importance for knowledge sharing between the volunteers.  We conducted qualitative semi structured interviews to collect empirical data, which was analysed through thematic analysis and the knowledge theories SECI model and the Concept Ba. From the thematic analysis six themes have emerged: organisational structure, commitment, information and communication technology, education, experience and relationships. These themes are the most important factors influencing knowledge sharing in the investigated organisation. Our results show that virtual volunteers share knowledge both physically and virtually. However, technical and organisational difficulties such as outdated documents and the volunteers' different possibilities to share knowledge with each other, were identified as challenges. We believe challenges with knowledge sharing in the organisation can be addressed by a Knowledge Management initiative adapted to the organisation including technical solutions facilitating flexible meetings, document management and a contact list of all volunteers and their role in the organisation. We suggest that implementation of a mentorship program would be beneficial for the organisation when new volunteers are introduced.