Agreements about sex with outside partners are common among gay couples, and breaks in these agreements can be indicative of HIV risk. Using longitudinal survey data from both partners in 263 HIV-negative and -discordant gay couples, we investigate whether relationship dynamics are associated with broken agreements. Twenty-three percent of respondents reported broken agreements. Partners with higher levels of trust, communication, commitment, and social support were significantly less likely to report breaking their agreement. Promoting positive relationship dynamics as part of HIV prevention interventions for gay couples provides the opportunity to minimize the occurrence of broken agreements and, ultimately, reduce HIV risk. © 2011 Springer Science+Business Media, LLC.