Infection with chlamydia increases the risk of pelvic inflammatory disease (PID), ectopic pregnancy and tubal factor infertility by at least 30%, a nationwide study from Denmark has shown. The risk persisted throughout the 17 years of follow-up. Following a second infection the risk of PID was increased by a further 20%. Adjusted hazard ratio for each reproductive complication was 31-50% higher in women who tested positive for chlamydia compared with women who tested negative.