This chapter discusses complications of rhinologic disorders, where sinusitis is a term that denotes presence of inflammation of the paranasal sinus mucosa. Therapies treating sinusitis aim to decrease the inflammation with topical and oral steroids, nasal irrigations, and antibiotics. Patients in an immune suppressed state are at higher risk for developing complications from seemingly typical sinusitis especially when fungus is involved. Access of pathogens into the intracranial vault can culminate in life-threatening conditions such as meningitis and intracranial abscess. Necrotic tissue or black eschar may indicate invasive fungal sinusitis and must be biopsied emergently. Serologic testing includes complete blood count with cell differential, glucose, erythrocyte sedimentation rate, C-reactive protein, and blood culture. Magnetic resonance imaging is superior to computed tomography for evaluation of the soft tissue and provides better detail regarding intracranial and skull base structures. Culture of nasal or ocular discharge guides targeted antibacterial therapy.