The diagnosis of chronic sinusitis is based on clinical presentation, nasal endoscopy and CT scan. As a matter of fact, the CT scan of the paranasal sinuses is absolutely necessary to characterise the lesions, to visualise anatomic variations which are risk factors for the endoscopic surgery and to follow up treated and/or operated patients with recurrent symptoms. Nowadays, plain films of paranasal sinuses do not have any indication. MR Imaging may be indicated in selected cases of complicated sinusitis and of pseudotumors associated to sinusitis.