Introduction: A breast abscess is a localised collection of pus within the breast that usually occurs as a complication of mastitis. Mastitis is an inflammation of breast tissue, which may or may not result from infection. Infective mastitis in lactating women is usually associated with Staphylococcus aureus (S. aureus), an organism which characteristically causes abscess development. Objectives: To report the incidence of breast abscess in lactating women. Materials and Methods: A randomised controlled trial and a survey study was carried out Dept. of Surgery, Sheikh Hasina Medical College and Hospital, Tangail, Bangladesh from January 2019 to December 2020. A total of 596 of 656 (91%) primiparous, Bangla-speaking women from a diverse range of backgrounds, including those receiving public clinic care, private care and birth centre care. An interview was conducted on breastfeeding at 24 months postpartum. Main outcome measures: Lactational mastitis and breast abscess. Results: One hundred and three women experienced mastitis. Three women developed a breast abscess: 0.4% of women who commenced breastfeeding (95% CI 0.14 – 0.98); 2.9% of women who took antibiotics for mastitis (95% CI 1.0– 6.7). Conclusion: Although many authors estimate that 11% of women with mastitis develop a breast abscess, the incidence of lactating breast abscesses appears to be lower than reported in the past. Our estimate is that 3% of women with mastitis will develop a breast abscess.