OBJECTIVE Bibliographic data for the management of acute mastoiditis in infants aged six months or less are very limited. This study investigated the presenting symptomatology, diagnostic and treatment options, and final outcomes in this age group. METHODS A retrospective review was conducted of all infants aged six months or less suffering from acute mastoiditis, admitted to our department between 2007 and 2017. RESULTS Eleven infants were identified. All of them developed the typical symptomatology of acute mastoiditis, while a higher rate of subperiosteal abscess formation was observed. Imaging was necessary in three cases only. Parenteral antibiotics and myringotomy were applied in all infants. A drainage procedure was also included in the infants with a subperiosteal abscess. Antrotomy was reserved for non-responsive cases. No intracranial complications were observed. All infants were cured without further complications or sequelae. CONCLUSIONS Acute mastoiditis in infants aged six months or less can be safely diagnosed and treated using a standardised algorithmic approach, similar to that used for older children.