Acute rhinosinusitis in children is a common disorder that is characterized by some or all of the following symptoms: fever, rhinorrhea, nasal congestion, cough, postnasal drainage, and facial pain/headache. It often starts as an upper respiratory tract infection that is complicated by a bacterial infection in which the symptoms worsen, persist, or are particularly severe. The accurate diagnosis of acute rhinosinusitis is challenging because of the overlap of symptoms with other common diseases, heavy reliance on subjective reporting of symptoms by the parents, and difficulties related to the physical examination of the child. Antibiotics are the mainstay of treatment. There is no strong evidence for the use of ancillary therapy. Orbital and intracranial complications may occur and are best treated early and aggressively. This article reviews the diagnosis, pathophysiology, bacteriology, treatment, and complications of acute rhinosinusitis in children.