This project examined whether interpersonal pressure to be muscular predicted late adolescents’ pursuit of muscularity. Participants were 199 adolescents (16—19 years), mothers (n = 175), and friends (n = 159), assessed at two annual times. Pressure to be muscular was assessed with adolescents’, mothers’, and friends’ reports of their relationships. Adolescents reported pressure from fathers and romantic partners, appearance satisfaction, disordered eating, and pursuit of muscularity. Adolescents’, mothers’, and friends’ reports of pressure related to pursuit of muscularity at both times. Adolescents’ perceptions and mothers’ reports prospectively predicted pursuit of muscularity. Findings highlight the relevance of relationships to pursuit of muscularity in late adolescents.