In December 2018, the AETIONOMY project reached the end of its funded period. The challenge that we faced when we started the project five years ago was more than ambitious. Specifically we set out to create a mechanism-based taxonomy for two neurodegenerative diseases that are known to be idiopathic – which means, that the aetiologies of the diseases are unknown. However, we have come close enough to meeting the goal of the project to share and celebrate its achievements, hence the organization of the final symposium of the AETIONOMY project.