In my presentation, I shall give an overview over the calendar system among the Kayan, a group living at the North coast of Papua New Guinea. Their ‘traditional’ calendar had far-reaching implications not only on the temporal structuring of daily life but also on many religious aspects and even on the settlement structure. With arrival of the first long-term missionaries, this calendar was replaced with the Gregorian calendar and many of the relating elements have disappeared. In order to be able to explain those parts of the system that are still in existence, I have tried to redraw a picture of the pre-mission calendar-based cosmology of the Kayan. My ethnography is person-centred and retrospective in many ways, the source of most of the stories being the old man Blasius Jong. His version, which can only represent one of many possible alternative stories, will be the first ‘preserved’ story of Kayan, thus having a deep impact on the way ‘traditional’ knowledge will be handled. Addressing the problems arising out of this situation may become part of the discussion.