While obtaining voluntary informed consent from patients with chronic obstructive pulmonary disease (COPD), bronchial asthma and patients presenting with psychiatric symptomology who participate in clinical trials, it is necessary to remember not only about the rights and ethical standards, but also about an extremely vulnerable position of the participants due to their disease specificity. Changes in the mental status of the patients and principal problems of every patient need to be considered. In this article, the aspects of obtaining informed consent from patients with respiratory diseases such as bronchial asthma and COPD and those under psychiatric supervision are reviewed. Apart from general recommendations, every category of patients has its own specific features. Being aware of them will improve doctor-patient communication.