BACKGROUND Breast milk is occasionally considered as a potential source of neonatal infection. Only a few cases of transmission of Streptococcus agalactiae (GBS) through breast milk have been published. The incidence of GBS in breast milk varies among studies. The incidence of GBS in breast milk in mothers with positive prenatal vaginal swabs for GBS is not known. OBJECTIVE The objective of this study was to compare the incidence of GBS in the breast milk of women colonized with GBS before delivery (GBS vaginal swabs positive) and women non-colonized with GBS (GBS negative) during the first week after term delivery. METHODS Breast milk from our sample of women was checked for the presence of GBS. A sample of 5 ml of breast milk was collected from each woman between days 3 and 7 after term delivery. Statistical analysis was carried out to test the relationship between bacterial content and GBS status of the women. RESULTS We identified only 2 of 243 (0.82%) GBS positive breast milk cultures during the study, both in the GBS negative group. There was found to be no GBS positive breast milk in women with positive prenatal vaginal swabs for GBS. CONCLUSION The incidence of GBS positive cultures in breast milk in the study was low. When comparing the incidence of GBS positive breast milk cultures between women colonized with GBS before delivery and women non-colonized with GBS, we identified only 2 GBS positive breast milk cultures, both in GBS non-colonized women.