The purpose of this research was to examine the immediate effects of engaging in predominantly positively or predominantly negatively valenced thinking about one’s most recent romantic ex-relationship and assess whether these effects are unique from thinking about memories from a non-romantic relationship. The application of self-regulation theory within the context of rumination and romantic relationship breakups suggests that recalling positive memories from a relationship may make it more difficult to move on from the relationship that ended, whereas recalling negative memories may make moving on easier. Participants were instructed to write about a relationship memory, with experimental manipulations of the memory valence (positive vs. negative) and relationship type (ex-relationship vs. friendship). Differences in outcome measures associated with adaptive and adverse breakup adjustment were subsequently examined. It was predicted that negatively valenced writing would yield higher ratings of adaptive adjustment measures and lower scores of adverse adjustment measures among participants in the ex-relationship condition, but yield lower scores of adaptive adjustment and higher scores on adverse adjustment among participants in the friendship condition. Results partially supported the hypotheses; participant ratings of adaptive outcomes were higher in the negative ex-relationship condition relative to the positive ex-relationship condition, and participants in the positive friendship condition higher ratings compared to those in the negative friendship condition. No meaningful differences were found with regard to adverse outcomes.