Over the last 20 years or so, aeropalynologic and allergologic studies have progressed and extensive international networks now provide regular pollen and hay-fever forecasts. To make a diagnosis of pollinosis, it is necessary to know the vegetation in the region where the patient lives. In Korea, pollen allergens that are considered to be clinically important are tree pollens in spring, grass pollens in summer, and weed in autumn. Pollination starts in spring and ends in autumn. Weed pollen is by far the most important cause of pollinosis in Korea peninsula, however, the most important pollen in Jeju island is from Japanese cedar in spring. The major clinical manifestations by pollen is allergic rhinitis and conjunctivitis. Bronchial asthma also develops in some of pollen-sensitized patients. The most important diagnostic approach is allergen skin prick test followed by serum-specific IgE measurement. To confirm the causative pollens, nasal and bronchial provocation test should be done. If the causative allergen is clarified, the treatment is to use a special mask in outdoor and keep stay inside of house equipped with an air filtration system if possible. To start preventive drugs just before the pollen season and continue them after the season is also an important therapy. Immunotherapy is recommended to the patients by consulting to an allergy specialist.