Figure 2 summarises the identification and exclusion of cases; 4724 women with a first coded episode of PID during the study period were identified from a population of 2.8 million woman-years of observation. Of these, 927 had evidence of a recent pregnancy and were excluded, leaving 3797 cases for the incidence analyses. The median age of the included women was 25 years (interquartile range 20–31 years).