This article advocates an understanding of ‘positioning’ as a key to the analysis of identities in interaction within the methodological framework of conversation analysis. Building on research by Bamberg, Georgakopoulou and others, a performative, interaction-based approach to positioning is outlined and compared to membership categorization analysis. An interactional episode involving mock stories to reveal and reproach an inadequate identity-claim of a co-participant is analysed both in terms of practices of membership categorization and positioning. It is concluded that membership categorization is a core element of positioning. Still, positioning goes beyond membership categorization in a) revealing biographical dimensions accomplished by narration and b) by uncovering implicit performative claims of identity, which are not established by categorization or description.