Background: The olfactory dysfunction that occurs during a COVID-19 infection has sparked much debate about its similarity to sinusitis. Up to 65% of COVID-19 pediatric patients may be asymptomatic; however, when symptoms are observed, fever and cough are the most common. Nasal congestion and discharge as well as headaches can also be seen, which makes both entities, i.e., COVID-19 and sinusitis, similar to each other. Methods: In this review, we present the clinical case of a teenager with a history of acute sinusitis and COVID-19 co-infection followed by purulent meningoencephalitis. We aim to summarize available findings on the association between COVID-19, sinusitis, and possible common complications of both diseases. Results: Differentiating between COVID-19 and sinusitis can be confusing because presented symptoms may overlap or mimic each other. Increased risk of complications, especially in patients with bacterial sinusitis co-infected with SARS-CoV-2, should prompt physicians to monitor young patients and inform parents about disturbing symptoms and possible complications. Conclusions: Acute sinusitis and COVID-19 co-infection may lead to numerous complications and should be included among the factors predisposing to worse prognosis. It is especially related to patients with high risk factors and even more important in children as they often pass the infection asymptomatically and its complications can lead to loss of health or life. Keywords: children; COVID-19; SARS-CoV-2; neurological manifestations; sinusitis; complications; abscess; thrombotic complications