The World Health Organization has emphasised the importance of HIV testing for couples as part of a global strategy to support the HIV prevention needs of couples, particularly those whose test results are ‘serodiscordant’ (one partner is diagnosed HIV-positive, the other HIV-negative). Studies have focused on motivations and barriers to testing together as a couple. However, this provides only partial insights into a bigger and often more complex story. In addition, little is known about whether HIV-negative partners continue to test for HIV. We focus on the preludes and aftermaths to HIV testing that can make up the serodiscordant chain of events, drawing on qualitative interviews with people in serodiscordant relationships in Papua New Guinea (PNG). Inspired by sociological/anthropological conceptualisations of diagnosis as relational and composite, our analysis seeks to trace the unfolding events before and after couples discover their mixed HIV status and, by so doing, generate initial insights into the contexts of HIV testing and serodiscordance in PNG. We argue that to understand HIV testing practices among couples, we need to understand the localised and syncretised meanings they bring to their serostatus.