Cerebral venous sinus thrombosis in children is a rare complication of acute mastoiditis that can potentially be fatal. Clinical expertise is essential for early diagnosis and management due to its subtle course. We present the first known case of paediatric acute mastoiditis with venous sinus thrombosis caused by Shewanella algae and Actinomyces europaeus . A 17-year-old male presented clinical signs of right acute otitis media and mastoiditis. Brain computed tomography showed mastoid opacification, cerebral sinus thrombosis and an extradural collection. Microbiology revealed the presence of S. algae and A. europaeus . A multidisciplinary approach combining medical and surgical treatment allowed the patient to make a full recovery.