Sigmoid sinus thrombosis following mastoiditis is a rare, but potentially life-threatening, condition. Its treatment usually consists of systemic antibiotics and mastoidectomy. In this report, we describe a pediatric case of sigmoid sinus thrombosis following mastoiditis, presenting with nonspecific symptoms such as fever, otalgia, and headache. Diagnosis was based on magnetic resonance imaging. The patient responded very well to intravenous antibiotics with a rapid clinical improvement and complete recanalization of the thrombosed sigmoid sinus. In conclusion, mastoiditis may present few clinical symptoms. In case of treatment failure or new onset neurologic deficit in children with acute otitis media, life-threatening complications associated with mastoiditis should be considered. Early diagnosis is important, as favorable prognosis can be achieved with conservative management without performing any surgical intervention.