Objective: Our goal was to determine the persistence of human papillomavirus infection of the cervix in a prospectively evaluated cohort of pregnant women observed from the first trimester until after delivery. Study Design: A group of 232 women were enrolled in the first trimester of pregnancy and had cervico-vaginal lavage specimens collected for detection of the deoxyribonucleic acid of human papillomavirus. They underwent sampling again in the third trimester (146 patients available) and at 4 to 12 weeks after delivery (83 patients available). Human papillomavirus deoxyribonucleic acid was detected by means of the Hybrid Capture assay. Results: In the first trimester of pregnancy, 31% of the patients had positive test results for human papillomavirus deoxyribonucleic acid, whereas 35.6% had positive results in the third trimester (P = 1.0). A comparison of first-trimester test results with postpartum results (paired data available from 83 patients) showed a decline from 39.8% positivity to 26.5% (P = .04). Comparing third-trimester results with postpartum results (paired data available from 74 patients) showed a decline from 35.1% to 25.7% positivity (P = .12). When specimens positive for human papillomavirus were divided between those containing “high cancer risk” types (9 virus types often associated with dysplasia or malignancy) and “low cancer risk” types (5 types usually found in benign lesions), similar trends were seen, although not all comparisons were statistically significant. Conclusion: The increased prevalence, during pregnancy, of detectable human papillomavirus deoxyribonucleic acid, which was previously reported (Fife et al, Am J Obstet Gynecol 1996;174:1487-93), persists at a similar level throughout pregnancy but declines in the postpartum period. This observation is most consistent with activation of the virus by the physiologic changes of pregnancy. (Am J Obstet Gynecol 1999;180:1110-4.)