Objective: To determine whether the 1996 consensus guidelines for prevention of early-onset group B streptococcal disease developed by the Centers for Disease Control and Prevention, ACOG, and the American Academy of Pediatrics are affecting obstetric practice and disease occurrence. Methods: Personnel in hospitals with obstetric services in seven surveillance areas completed surveys about their programs, patient populations, and group B streptococcal disease prevention policies. Survey results were linked to group B streptococcal disease cases identified by active surveillance in 1996 and 1997. An early onset case was defined as a case in which group B streptococci were isolated from a sterile site in the 1st 6 days of life. The number of cases in 1996 and 1997 were compared using a paired t test. Linear regression was used to assess hospital characteristics associated with group B streptococcal disease cases. Results: Of 177 hospitals, 165 (93%) responded, and 96 (58%) of those had group B streptococcal disease prevention policies. Hospitals that established or revised their policies in 1996 had a lower mean number of cases in 1997 than in 1996 (0.58 versus 1.29, P = .006). Linear regression analysis, controlling for number of births, indicated that a hospital’s having more black mothers and location in particular states were associated with more cases of disease. Citing the 1996 ACOG reference as the source for hospital group B streptococcal disease prevention policy was associated with fewer cases of group B streptococcal disease (P = .038). Conclusion: The publication and adoption of the guidelines were associated with decreasing occurrence of group B streptococcal disease. (Obstet Gynecol 2000;95:377–82.)