Hypersensitivity pneumonitis (HP) is more common in middle-aged individuals but has been also diagnosed in patients of all ages including infants and children. Host risk factors are poorly characterized. The aim of this paper is presentation of 6 young patients in whom HP was diagnosed at the stage of lung fibrosis.There were 5 females at the age of 16-35 years and 1 male at the age of 28 years. All of them were exposed to organic dust for many years. Three of them were asthenic with scoliosis, 5 had clubbing. All patients were released from sport exercises in school due to fatique but the diagnostic procedures were started at that time only in 2 patients. One woman had been ill from early childhood ( recurrent pneumonia was recognised). In the another girl (16 years old) the spontaneous pneumothorax was the cause of the first chest X-ray examination. In the next woman (21 years old) marked dyspnea was connected with pregnancy and massive fibrotic lesions were recognised after delivery of her child . The only man was diagnosed before change of his job; he had no complaints. Two oldest women (34 and 35 years old) were diagnosed in childhood but avoidance of antigen exposure and corticotherapy were not effective. In all patients precipitins against farmer's lung and pigeon fancier's lung antigens were found. In all patients chest X-ray showed features of advanced lung fibrosis.All patients were treated with steroids without improvement. Two patients died during corticotherapy Conclusions: 1) HP could be taken into consideration during differential diagnosis of interstitial lung diseases, 2) Cough and dyspnea on exertion could be the firstsymptomsof chronic HP in children also.