The task of physicians is to take a holistic view of patients, taking into account not only the main diseases, but also risk factors worsening their prognosis. Respiratory diseases are among the most important diseases in the clinical practice. In the course of chronic obstructive pulmonary disease, lung cancer, and respiratory tract infections undernutrition is often observed. This can be the result of disease itself but also the risk factor in disease development. Malnutrition is frequently observed in the course of chronic respiratory diseases. Physicians should regularly assess the nutritional status in these cases using appropriate medical history and anthropometrical measurements. Diagnosed underweight or cachexia require implementation of adequate nutrition taking into account specificity of respiratory diseases. If nutritional problems are not identified and appropriate treatment is not prescribed it will be difficult to expect good remote results of treatment of chronic respiratory system diseases.