Objective: To determine the antibiotic sensitivity patterns of rectovaginal group B streptococcal (GBS) isolates obtained from a heterogeneous obstetric population in the late third trimester. Methods: We performed a prospective observational study of rectovaginal GBS isolates obtained in the late third trimester during routine screening between January and December 1998. All cultures were prepared in a selective broth medium for 18–24 hours before plating onto sheep blood agar. Susceptibility testing of all isolates was performed for ampicillin, cefazolin, clindamycin, erythromycin, penicillin G, and vancomycin using the Vitek GPS card method. Results: A total of 2,111 rectovaginal cultures were performed in which GBS was isolate from 574 (27.2%) patients. The antibiogram of percent susceptible is as follows: vancomycin (100%), ampicillin (98.2%), penicillin G (98.2%), cefazolin (98.2%), clindamycin (92%), and erythromycin (81%). Ten isolates (1.8%) were sensitive only to vancomycin. Conclusions: Routine susceptibility testing of GBS isolates collected during pregnancy should be considered due to the emergence of antibiotic resistance among GBS strains.