Background: Individuals who repeatedly acquire sexually transmitted infections (STIs) may facilitate the persistence of disease at endemic levels. Identifying those most likely to become reinfected with an STI would help in the development of targeted interventions. Goal: To investigate the demographic and behavior characteristics of sexually transmitted disease (STD) clinic patients most likely to reattend with an STI. Study Design: The proportion of patients attending three STD clinics in England between 1994 and 1998 who reattended for treatment of acute STI within 1 year was estimated from Kaplan-Meier failure curves. A Cox proportional hazard model was used to investigate the relation between rate of reattendance with an acute STI and patient characteristics. Results: Of the 17,466 patients presenting at an STD clinic with an acute STI, 14% reattended for treatment of an STI within 1 year. Important determinants of reinfection were age, sexual orientation, and ethnicity: 20% of 12- to 15-year-old females (adjusted hazard ratio [HR], 1.90; CI, 1.13-3.18, compared with 20- to 24-year-old females), 22% of homosexual men (adjusted HR, 1.30; CI, 1.07-1.58, compared with heterosexual men), and 25 % of black Caribbean attendees (adjusted HR, 1.87; CI, 1.63-2.13, compared with whites) reattended for treatment of acute STI within 1 year. In addition, 21% of those with a history of STI (adjusted HR, 1.42; CI, 1.28-1.59, compared with those with no history of STI) and 17% of individuals reporting three or more partners in the recent past (adjusted HR, 1.53; CI, 1.34-1.73, compared with those with one partner) reattended for treatment of an acute STI within 1 year.