Abstract: We critically reviewed randomized controlled trials evaluating chlamydia screening to prevent pelvic inflammatory disease (PID) and explored factors affecting interpretation and translation of trial data into public health prevention. Taken together, data from these trials offer evidence that chlamydia screening and treatment is an important and useful intervention to reduce the risk of PID among young women. However, the magnitude of benefit to be expected from screening may have been overestimated based on the earliest trials. It is likely that chlamydia screening programs have contributed to declines in PID incidence through shortening prevalent infections, although the magnitude of their contribution remains unclear. Program factors such as screening coverage as well as natural history factors such as risk of PID after repeat chlamydia infection can be important in determining the impact of chlamydia screening on PID incidence in a population. Uptake of chlamydia screening is currently suboptimal, and expansion of screening among young, sexually active women remains a priority. To reduce transmission and repeat infections, implementation of efficient strategies to treat partners of infected women is also essential. Results of ongoing randomized evaluations of the effect of screening on community-wide chlamydia prevalence and PID will also be valuable.