The anatomical relationships of the middle ear, the mastoid air cells, the temporal bone and intracranial structures can lead to invasive infections. Acute mastoiditis is the most common intratemporal complication of acute otitis media. Timely management includes antimicrobial therapy, imaging including ultrasound and/or computed tomography, surgical consultation and intervention. There are insufficient data to provide an evidence-based diagnostic tool for acute mastoiditis. Clinical, laboratory and microbiological differences between children with simple and complicated mastoiditis will be explored after case presentation of a 5-year-old boy with fever and a tender, soft-tissue swelling over the left zygomatic arch.