Lung cancer is the most common malignancy in the world and frequency of allergic diseases increases especially in high-developed countries. In the literature there have been published articles about association between lung cancer and allergic diseases, which don't give a simple answer if there is any connection between them. The aim of this study was the assessment of frequency of allergy in patients with lung cancer. The study was based on medical records and questionnaire performed among patients hospitalized in Department of Pneumonology and Allergology Medical University of Warsaw and in Department of Thoracic Surgery Institute of Tuberculosis in Warsaw. The study included 113 patients (30 women and 83 men). Coexistence of allergy with primary lung cancer was observed in 7 cases which makes 6.2% (frequency of: asthma 1.8%, allergy to drugs 3.5%, allergy to animal's dander 0.9%). The result of this examination reveals that there is significant lower frequency of allergic diseases in patients with lung cancer in comparison with frequency of allergic diseases in adult population of Poland estimated at 15.8%.