BACKGROUND Brain abscesses are very rarely diagnosed in neonates, but if present, they are associated with a high risk of severe complications and mortality. In neonates, brain abscesses can be detected on transfontanelle ultrasonography, in which they appear as hyperechogenic lesions surrounded by a hypoechogenic border. METHODS We present a female neonate, born in the 28th week of gestation, with birth weight of 950 grams, who was born in an ambulance by spontaneous vaginal vertex delivery. No signs of infection were present until the 35th day of hospitalization, when a sudden and serious deterioration in the patient's condition was observed due to late-onset sepsis. Cranial US, performed on the 40th day of life, revealed hyperechogenic lesions with a hypoechogenic halo in the right frontal lobe, which could correspond to brain abscesses. These lesions were caused by Citrobacter koseri septicaemia, identified by transfontanelle ultrasonography, and confirmed on magnetic resonance imaging. The patient recovered and was discharged on the 91th day of life (39 PCA) with a recommendation of permanent neurological surveillance. CONCLUSIONS Ultrasonography of the central nervous system can reveal inflammatory changes and developing brain abscesses. In neonates, magnetic resonance imaging should be performed as the method of choice for confirming brain abscesses.