To study the association of pelvic inflammatory disease and various types of intrauterine devices (IUDs), data from the Women's Health Study were analyzed. The analysis included data from interviews of 622 women hospitalized with an initial episode of pelvic inflammatory disease and 2369 hospitalized control subjects reporting no history of pelvic inflammatory disease. Compared to the risk in women using no contraception, the relative risk of pelvic inflammatory disease in women currently using the Dalkon Shield was 8.3 (95% confidence limits 4.7 to 14.5). This represented a fivefold increase in risk compared to women currently using other types of IUDs. In this study, only 10% of women wearing an IUD were using the Dalkon Shield, yet they accounted for almost 20% of the excess risk of pelvic inflammatory disease occurring among all the IUD users. Most of the increased risk of pelvic inflammatory disease for women currently using other IUDs (excluding the Dalkon Shield) occurred in the first four months after insertion. These associations were not explained by differences between cases and controls in demographic variables, level of sexual activity, or medical history. The authors recommend that women still using a Dalkon Shield have it removed.