How do sex risk and protection change over the course of a relationship? It is often claimed that protection generally declines over the course of relationships. This 3-year longitudinal study examines 412 new sexual relationships described by 126 adult participants and tests this claim. Analyses identify four relationship trajectories: only 15% of new sex relationships show a declining trajectory of protection; another 12% show only a temporary decline. Population average analyses previously interpreted to show a decline in protection are shown here to be is largely explained by the attrition of the low trust, high protection relationships that creates the association between higher trust and lower protection. The long-term relationships turn out mostly