Although previous research has examined associations among masculinity, sexual orientation, minority stress, and mental health, these studies focused exclusively on individuals as units of analysis. This study investigates how men in same-sex relationships uniquely experience minority stress associated with their perceptions and performances of masculinity, as individuals and as couples. Qualitative, dyadic data are drawn from in-depth interviews with 24 male couples (48 partners), discussing two main stress themes—Threatened by Others’ Gender Performances and Straight-acting Masculinity as Individual-level Insulation with Couple-level Challenges. Primary findings are (1) men in same-sex relationships are vulnerable to new forms of minority stress because their relationships increase visibility via others’ masculinity, and (2) being in a same-sex relationship influences partners’ self-perceptions of masculinity and their relationship dynamics. Findings improve insights regarding gender performance in minority stress processes affecting sexual minority men and their intimate relationships with one another. By virtue of their sexual minority and relationship statuses, men in same-sex relationships experience unique, masculinity-related stressors.