Fungus balls of the paranasal sinuses represent a noninvasive manifestation of fungal sinusitis. Patients are immunocompetent but no more allergic than the general population. There is little tissue reaction to the tangled mat of hyphae. If the patient becomes immunocompromised, then the fungus ball may become invasive, as illustrated by an included case report. One hundred sixty-three additional cases of patients with paranasal sinus fungus balls are reviewed from the literature.