Objective: This study was undertaken to determine whether endometrial microbial colonization or plasma cell endometritis is increased after spontaneous versus indicated preterm delivery or a spontaneous term delivery. Study design: Postpartum, endometrial specimens were obtained after a spontaneous (mean 83, ± 17.6 days) or indicated (mean 83, ± 16.7 days) preterm delivery before 34 weeks' gestation and after a spontaneous term delivery (mean 82, ± 15.7 days; P = .980). Cultures for aerobic and anaerobic bacteria, Trichomonas vaginalis, and genital mycoplasmas were performed. Histologic endometritis was defined as the presence of plasma cells. Results: The study population (n = 820) was 71% black, 29% white, 69% unmarried, and 31% had less than 12 years of education. Endometrial cultures were positive for at least 1 microorganism in 82% of the women. No significant difference in positive endometrial cultures were observed among women after a spontaneous versus an indicated preterm delivery (85% vs 79%, P = .102), or a spontaneous preterm versus a spontaneous term delivery (85% vs 81%, P = .123). Plasma cell endometritis was present in 39% of 506 specimens sufficient for histologic examination and was also similar in the three groups (P = .160). Conclusion: Microbial colonization of the endometrium and plasma cell endometritis are similar 3 months after spontaneous or indicated preterm or term births. Therefore, chronic infection and inflammation of the endometrium (documented at 3 months postpartum) do not appear to be risk factors for subsequent delivery in women with a prior spontaneous delivery less than 34 weeks' gestation. © 2005 Mosby, Inc. All rights reserved.