To estimate the proportion of group B streptococci (GBS)-colonized women with a reported penicillin allergy without anaphylaxis receiving appropriate intrapartum antibiotic prophylaxis.We performed a retrospective cohort study of GBS-colonized, penicillin-allergic women delivering at term receiving intrapartum antibiotic prophylaxis during labor. Scheduled cesarean deliveries were excluded. The primary outcome was the proportion of women who received appropriate antibiotic coverage, defined as penicillin or cefazolin. Secondary outcomes included neonatal outcomes such as Apgar score, blood draws, antibiotic use, length of hospital stay, and composite morbidity.Of 165 women reporting a penicillin allergy without anaphylaxis, 73 (44.2%) received an appropriate antibiotic and 92 (55.8%) received an inappropriate antibiotic. Of those receiving an inappropriate antibiotic, 56 (60.9%) were given clindamycin, 1 (1.1%) erythromycin, and 35 (38.0%) vancomycin. Women reporting rash as a penicillin reaction were more likely to receive cefazolin than another antibiotic (44 [60.3%] compared with 24 [26.1%], respectively; P<.001), whereas women whose reaction was not documented were less likely to receive cefazolin (18 [24.7%] compared with 63 [68.5%], respectively; P<.001). Among neonates whose mothers received appropriate compared with inappropriate antibiotics, there were no differences in Apgar score, number of blood draws, antibiotic use, length of hospital stay, or composite morbidity.More than half of women allergic to penicillin without anaphylaxis received an antibiotic other than penicillin or cefazolin as prophylaxis, indicating poor adherence to national guidelines.