This retrospective spontaneous report has been received from the author of a literature article and a meeting abstract. Background: In October 2012, the Advisory Committee on Immunization Practices (ACIP) recommended dose of Tdap during each pregnancy, irrespective of the woman's prior history of receiving Tdap. A retrospective cohort study to assess the safety of Tdap vaccination in pregnant women in two Vaccine Safety Datalink (VSD) sites during 2010-2012 found a small but statistically significant increased risk of chorioamnionitis. Objective: We conducted a review of the VAERS database to describe reports of chorioamnionitis following receipt of any vaccines. Methods: We searched the VAERS database for reports of chorioamnionitis after any vaccine during the period from July 1, 1990 through February 2, 2014. Conclusion: Chorioamnionitis was found to be uncommonly reported, representing 1% of pregnancy reports to VAERS. A majority of reports had at least one risk factor for chorioamnionitis. Clinical chorioamnionitis was defined as patients presenting with fever more than or equal to 38 degree Centigrade, and two or more of the following signs or symptoms: uterine tenderness, foul-smelling lochia, maternal tachycardia (>100 bpm), fetal tachycardia (>160 bpm), or maternal leukocytes (WBC >16,000 cells/mm3). Histological chorioamnionitis were those reports with pathology findings describing polymorphonuclear leukocytes on microscopic examination of placenta and fetal membranes. The largest number of reports (10/31: 32.3%) was received during the 2009-2010 influenza season. The most common vaccines (90%) documented in chorioamnionitis reports were inactivated vaccines, and the three most common were: H1N1, HPV4, and Tdap vaccines in 32%, 29% and 26% of reports, respectively. Fifty-eight percent of reports had at least one risk factor for chorioamnionitis. Seventy-four percent of reports had chorioamnionitis onset more than two weeks after vaccination. H1N1 vaccines were administered in all reports with an onset interval less than 2 weeks. Among the 13 reports with no risk factors for chorioamnionitis, 8 had clinical criteria for this condition and 5 had histological criteria. Adverse pregnancy and neonatal outcomes among chorioamnionitis reports included the following: nine (29%) reports of fetal death (3 spontaneous abortions and 6 stillbirths); 22 live births (71%) which included 6 (19%) reports of preterm birth and 16 (52%) reports of term birth; two (6%) reports of postpartum hemorrhage and one (3%) report of maternal admission to the intensive care unit (ICU). No maternal deaths were reported. Among the six preterm births, two resulted in infant deaths, one occurring soon after birth and the second required admission to the neonatal intensive care unit (ICU) for prematurity, sepsis, nutritional and breathing support, with death occurring one month after delivery. This report refers to one female patient of unknown age. Last menstrual period and expected date of delivery were unknown. On an unknown date the patient was vaccinated with MMR (manufacturer unknown) (lot#, dosage, frequency and route unspecified). Other suspect therapies included VARIVAX (Merck) (manufacturer, lot#, dosage, frequency and route unspecified). On an unknown date the patient experienced chorioamnionitis. The outcome of the event was unknown. The outcome of fetal and pregnancy was unknown. The reporter considered the event to be related to the vaccination. This is one of several reports received from the same literature article. Additional information has been requested.