Objective: To investigate the cost-effectiveness of accelerated partner therapy (APT) compared with standard contact tracing for people with sexually transmitted chlamydia infection in the United Kingdom Design: Economic evaluation using a model consisting of two components: a population-based chlamydia transmission component, to estimate the impact of APT on chlamydia prevalence, and an economic component, to estimate the impact of APT on healthcare costs and health outcomes. Setting: United Kingdom Participants: Hypothetical heterosexual population of 50,000 men and 50,000 women aged 16-34 years. Main Outcome Measures: Cost-effectiveness based on quality-adjusted life years (QALYs) gained and major outcomes averted (MOA), defined as mild pelvic inflammatory disease (PID), severe PID, chronic pelvic pain, ectopic pregnancy, tubal factor infertility and epididymitis. Results: For a model population of 50,000 men and 50,000 women and an APT intervention lasting 5 years, the intervention cost of APT (&pound135,201) is greater than the intervention cost of standard contact tracing (&pound116,334). When the costs of complications arising from chlamydia are considered, the total cost of APT (&pound370,657) is lower than standard contact tracing (&pound379,597). Thus, APT yields a total cost saving of approximately &pound9000 and leads to 73 fewer major outcomes and 21 fewer QALYs lost. Hence, APT is the dominant PN strategy. APT remained cost-effective across the full range of sensitivity analyses. Conclusions: Based on cost-effectiveness grounds APT is likely to be recommended as an alternative to standard contact tracing for chlamydia infection in the United Kingdom