Introduction: Neonatal mastitis is a rare infection. When it does occur, infants younger than 2 months of age are typically affected and the majority of cases are caused by Staphylococcus aureus. We present the first reported case of neonatal mastitis caused by Acinetobacter baumannii, an unusual organism for this type of infection. Case presentation: A 15-day-old full-term Caucasian male neonate presented to our emergency room following fever at home and was admitted for routine neonatal sepsis evaluation. After admission, he developed purulent drainage from his right nipple, was diagnosed with mastitis, and was started on empiric therapy with clindamycin and cefotaxime with presumed coverage for S. aureus. Drainage culture identified pan-susceptible Acinetobacter baumannii/haemolyticus and antibiotic therapy was changed to ceftazidime. He was discharged after 5 days of ceftazidime with complete resolution of his symptoms. Conclusions: This case illustrates the importance of obtaining drainage cultures in mastitis cases because of the possibility of organisms besides S. aureus causing infection. Acinetobacter baumannii is considered part of the normal human flora and is associated with serious infections in intensive care units. This is the first case report describing Acinetobacter baumannii as an etiologic agent of neonatal mastitis and highlights the importance of including unusual organisms in the differential for infectious etiologies for general practitioners.