Background: Ultrasound-guided percutaneous drainage has been suggested in recent years to be the treatment of choice for breast abscesses. Although MRSA has recently been observed to be a significant causative pathogen in mastitis, reports dealing with ultrasound-guided drainage of breast abscess did not address the bacteriology of these infections. Study Design: Between January 1 and December 31, 2007, 129 women were diagnosed with puerperal mastitis at Taipei City Hospital. Data were collected by retrospective chart review. Charts were surveyed for mastitis recurrence for at least 1 year after the initial infection treatment, through December 31, 2008. Results: The most commonly identified organism was Staphylococcus aureus, present in 69 of 78 of bacterial isolates (88%). There were 52 of 78 (66%) bacterial isolates that were MRSA. Forty-seven of 52 (90%) women infected by MRSA underwent initial ultrasound-guided percutaneous abscess drainage. Among them, 11 (23%) women underwent subsequent conversion to surgical incision and drainage. Comparing women infected with MRSA and women infected with other pathogens, there was no statistical difference in the duration of treatment, number of outpatient follow-up visits, duration of antibiotics use, or abscess recurrence rates. Conclusions: MRSA is the most common bacteria in puerperal breast abscess in our population. When these patients are treated initially by percutaneous abscess drainage followed by repeated ultrasound-guided drainage or surgical incision and drainage, the presence of MRSA may not adversely affect treatment outcomes.