Allergic rhinitis, the most common type of rhinitis, generally can be differentiated from the numerous types of nonallergic rhinitis through a thorough history and physical examination. Allergic rhinitis may be seasonal, perennial, or occupational. The most common cause of nonallergic rhinitis is acute viral infection. Other types of nonallergic rhinitis include vasomotor, hormonal, drug-induced, structural, and occupational (irritant) rhinitis, as well as rhinitis medicamentosa and nonallergic rhinitis with eosinophilia syndrome. Since 1998, three large expert panels have made recommendations for the diagnosis of allergic and nonallergic rhinitis. Allergy testing (e.g., percutaneous skin testing, radioallergosorbent testing) is not necessary in all patients but may be useful in ambiguous or complicated cases.