Epidemiology of pelvic inflammatory disease in parous women with special reference to intrauterine device use. Up to the end of 1989, 206 parous women in the Oxford Family Planning Association contraceptive study had been referred to hospital with a first episode of pelvic inflammatory disease. Of these, 65 suffered from definite disease described as acute, 81 from definite disease not described as acute and 60 from 'other disease'. Considering all forms of disease together, referral was less common in those aged 25-29 and in those aged 45 or more than in those aged 30-44. Referral was more common in those of low social class, in those who smoked and in those who married young. All these factors were taken into account in analyses considering the effects of contraceptive methods. In these analyses, women currently using the contraceptive pill, the diaphragm, the sheath, female sterilization or an intrauterine device (IUCD) were compared with those currently using other methods or no method of contraception. IUCD ex-users were, however, placed in a separate category, irrespective of their current method of contraception. The relative risks obtained in these analyses, with 95% CI, were as follows: contraceptive pill 0.5 (0.2-0.9), diaphragm 0.6 (0.3-1.2), sheath 1.2 (0.6-2.4), female sterilization 0.7 (0.3-1.5), non-medicated IUCD 3.3 (2.3-5.0), medicated IUCD 1.8 (0.8-4.0), IUCD ex-users 1.3 (0.7-2.3). These data suggest that oral contraceptives, the diaphragm and female sterilization protect against pelvic inflammatory disease and that IUCDs increase the risk. Medicated devices, however, appear to carry only about half the risk of non-medicated devices, and the elevation of risks in IUCD ex-users appears to be small. Special analyses examined the risk associated with use of a Dalkon Shield. Among women currently using an IUCD (of any kind), those who had used a Dalkon Shield (at any time) had nearly five times as great a risk of hospital referral for pelvic inflammatory disease as those who had never used a Dalkon Shield (relative risk 4.7, 95% CI 2.1-9.0). 