This chapter discusses chronic sinusitis and its complications, which is a chronic inflammation of mucous membrane which has resulted in irreversible, usually degenerative, changes. Factors predisposing to chronic sinusitis include anatomical deviated nasal septum, congenital, hypersensitivity, dental sepsis, poor resistance, alcohol, allergy, dusty environment, fungi and iatrogenic factors. A secondary infection results from chronic obstruction of the ostium and polyposis or as a sequel of acute infection. Fungal infection occurs mostly in traumatic cases with compound fractures, in uncontrolled diabetics, debilitated patients, such as carcinoma, and in patients on immunosuppressants, antibiotics or steroids. Mucocele of the ethmoid sinuses displaces the eyeball forwards and laterally, while mucocele of the frontal sinus displaces the eyeball forwards, downwards and laterally. Transillumination tests are done for maxillary and frontal sinuses by a special torch in a darkened room. Signs and symptoms, proof puncture, and radiography rarely leave any doubt in diagnosis.