The present study addresses gaps in the literature related to theory development for young men who have sex with men (YMSM) sexual practices through the application and modification of Social Action Theory. Data come from the Healthy Young Men study (N = 526), which longitudinally tracked a diverse cohort of YMSM ages 18-24 to characterize risk and protective factors associated with drug use and sexual practices. Structural equation modeling examined the applicability of, and any necessary modifications to a YMSM-focused version of Social Action Theory. The final model displayed excellent fit (CFI = 0.955, TLI = 0.947, RMSEA = 0.037) and suggested concordance between social support and personal capacity for sexual health promotion. For YMSM, practicing health promotion and avoiding practices that may put them at risk for HIV was associated with both social isolation and psychological distress (β = -0.372, t = -4.601, p<0.001); psychological distress is an internalized response to environmental and cognitive factors and sexual practices are an externalized response. Results point to the utility of Social Action Theory as a useful model for understanding sexual practices among YMSM, the application of which shows health protective sexual practices are a function of sociocognitive factors that are influenced by environmental contexts. Social Action Theory can help prevention scientists better address the needs of this vulnerable population.