To examine the relationship between cigarette smoking and pelvic inflammatory disease we analyzed data from a hospital-based, case-control study of pelvic inflammatory disease. Case subjects were 197 women hospitalized with their first episode of pelvic inflammatory disease; control subjects were 667 women hospitalized with nongynecologic conditions. Logistic regression was used to control for potentially confounding factors, including number of recent sexual partners, frequency of intercourse, and previous episodes of gonorrhea. Compared with women who had never smoked, current cigarette smokers had a significantly elevated relative risk of pelvic inflammatory disease of 1.7 (95% confidence interval, 1.1 to 2.5). Similarly, former cigarette smokers had a significantly elevated relative risk of pelvic inflammatory disease of 2.3 (95% confidence interval, 1.3 to 4.2). However, a dose-response relationship was not observed. These results suggest that cigarette smoking is associated with pelvic inflammatory disease. Whether or not this association is causal requires clarification. The high prevalence of cigarette smoking and the serious consequences of pelvic inflammatory disease make such clarification an important consideration for future research.