The clinical case of differential diagnosis of progressively worsening dyspnea reflects the complicated clinical situations when the patient diagnosis should be based on the differential diagnosis of the various organ systems disturbances in the patients with uncommon diseases. We present the clinical case of the idiopathic fibrosing alveolitis. This serious interstitial lung disease, although relatively rare, is becoming increasingly common. We would like to accentuate the essence of accurate interpretation of common clinical and laboratory investigations to be able to establish the diagnosis of the rare disease. New recommendations for the diagnosis and the treatment of this disorder are presented.