HIV disproportionately impacts men who have sex with men (MSM) in the USA. Building upon research on relationship constructs unique to MSM couples’ HIV-prevention needs, we developed two new scales measuring sexual agreement self-efficacy (SASE) and importance of sexual agreement communication (ISAC). Following qualitative item development, we used two large independent samples of MSM couples (N1 = 441, N2 = 388) to conduct scale validation. Exploratory factor analyses indicated both SASE and ISAC to be unidimensional with 7 and 5 items (eigenvalues = 5.68 and 3.50), respectively, with strong factor loadings. Confirmatory factor analyses yielded satisfactory model fit for SASE (CFI = 0.99; SRMR = 0.03) and ISAC (CFI = 0.99; SRMR = 0.05). Reliability was high for SASE (ω = 0.92) and ISAC (ω = 0.84). Predictive validity analysis revealed a protective association between higher scores on both scales and the outcomes of sexual risk behavior and agreement breaks. Convergent and discriminant validity analyses demonstrated associations in the expected directions between these scales and multiple measures of relationship quality. Therefore, SASE and ISAC are two brief, valid, and reliable scales that can facilitate more in-depth explorations of sexual agreements in MSM and thereby contribute greatly to improving our understanding of and ability to intervene on sexual agreements to improve health and relationship outcomes.