If you suspect you may have sinusitis, see the doctor to obtain a diagnosis and treatment if necessary. The doctor will take your personal and family medical history and will perform a physical examination. He or she may also order imaging studies to see inside the sinuses or other tests that can help aid in the diagnosis. When taking your history, the doctor will ask about the duration of your symptoms, any risk factors for sinusitis you may have (such as allergies), and your recent respiratory health (e.g. if you recently had a cold). During the examination, the doctor will likely touch places on your face and nose to see if they are tender and may look inside your nose for signs of inflammation.

Imaging techniques such as computerized tomography (CT) or magnetic resonance imaging (MRI) can show what is inside your sinuses and nasal area and can help identify inflammation or physical obstructions. In some cases, the doctor may use a nasal endoscope - a flexible tube with a fiber-optic light inserted through your nose — to inspect the inside of your nasal passages and sinuses.

If you have chronic (long lasting) or recurring sinusitis, the doctor may order laboratory tests such as nasal or sinus cultures that involve taking a small sample form inside the nose or sinus and culturing it in a Petri dish to see what kind of microorganisms are present. Your doctor may also suggest allergy testing, since people with allergies are prone to repeated occurrences of sinusitis. Allergy skin testing can help figure out the allergen or allergens responsible for your sinus symptoms.