OBJECTIVE: To identify opportunities to reduce overuse of antibiotics for prevention of perinatal group B streptococcal (GBS) disease and management of preterm premature rupture of membranes (pPROM). METHODS: An anonymous written questionnaire was sent to each of 1031 Fellows of the American College of Obstetricians and Gynecologists, and the responses were subjected to statistical analysis. RESULTS: Among those of the 404 respondents who saw obstetric patients in 2001, most (84%) screened for GBS colonization, and 22% of these prescribed prenatal antibiotics to try to eradicate GBS colonization. Of the 382 respondents (95%) who prescribed antibiotics for pPROM, 36% continued antibiotics for more than 7 days despite negative results from GBS cultures collected before initiation of treatment. Having more years of clinical experience (adjusted odds ratio (OR) 3.0, 95% confidence interval (CI) 1.5 to 6.2), working in a non-academic setting (adjusted OR 2.7, 95% CI 1.0 to 6.9), and prescribing antibiotics prenatally for GBS colonization (adjusted OR 2.0, 95% CI 1.1 to 3.4) were associated with prescribing prolonged antibiotics for pPROM. CONCLUSION: Prenatal antibiotic treatment for GBS colonization and prolonged antibiotic treatment for pPROM contribute to overuse of antibiotics in obstetrics.