Research has shown that attachment-related events such as a romantic relationship break-up can activate and/or make more salient the cognitions, affect, and behaviors associated with attachment style. Research has also shown that security primes, which seek to increase the degree of attachment security, can help to mitigate the degree to which insecure attachment style negatively affects key processes and outcomes. The current study tested the impact of attachment style and/or security primes on a single-session expressive writing task. Participants were roughly 150 undergraduates (the actual sample size varied somewhat by the hypotheses) who had recently experienced a romantic relationship break-up were randomly assigned to one of the following three conditions: (a) an expressive writing only task in which participants were asked to delve into their deepest thoughts and feeling related to the break-up, (b) a writing + prime task in which participants were exposed to a security prime prior to the expressive writing task, (c) a control writing task. The goals of this study were, first, to investigate whether or not the writing samples would reflect participants' attachment styles and, second, to examine the extent to which attachment style or the security prime would affect the results of the expressive writing interventions. Results revealed that attachment style and the security prime did not generally affect the degree to which the expressive writing task promoted psychological and physical health functioning. However, supplementary analysis suggested that attachment style and the security prime did affect some indices of psychological or physical health functioning in a subsample of participants whose ex-partner had reportedly initiated the break-up. Additionally, results reveal that participants' attachment style was reflected in the content of the writing samples.