Consensual non-monogamous (CNM) relationship rules, the boundaries and understandings partners have about acceptable behaviors related to their CNM relationship, are associated with relationship functioning and sexual health risk among gay and bisexual men. Partnered young gay and bisexual men (YGBM) experience unique relational challenges and sexual health disparities. Thus, understanding the nuances of relationship rules among YGBM in CNM relationships is of particular importance. However, few studies have examined relationship rules specifically among YGBM. The current study sought to explore relationship rules among YGBM in CNM relationships, including both those explicitly discussed and those implicitly assumed. We also assessed concordance and discrepancies in partners’ reports of their relationship rules, as well as rule violations. Partners from 10 CNM couples (n = 20; Mage = 25.3) completed separate semi-structured interviews that included questions about their relationship rules. Individual- and dyad-level analyses were conducted using a modified version of the consensual qualitative research method. Three main themes of relationship rules emerged from the data: extradyadic partner criteria, conditions regarding extradyadic sex, and conditions regarding maintenance of the primary relationship. While 39% of participants reported rules that were not endorsed by their partner, few clearly contradictory discrepancies in partners’ reports were observed. Nine participants reported having at least one implicit rule and 70% of participants (from 8 of 10 couples) reported that they and/or their partner violated at least one rule. Explicit rules and rule concordance may be associated with improved relationship functioning. Common violations of sexual risk reduction rules may contribute to YGBM’s increased HIV/STI risk.