The aim of the study is to illustrate the case reports of patients with catamenial pneumothorax and with consecutive discussion about the causes of late diagnosis of endometriosis and recurrence of pneumothorax.Material and methods. Three own clinical cases of middle-aged women with catamenial pneumothorax who were treated in the surgical thoracic department of the «Samara Regional Clinical Hospital named after V.D. Seredavina» in 2017 had been described.Results. In all clinical cases the pleuroperitoneal fistula was the direct cause of the development of pneumothorax due to the germination of the endometrial node. The lack of caution regarding endometriosis leads to the fact that the revision of the diaphragm during thoracoscopy is performed rarely and very superficially. The solution about the volume of diaphragm repair is simple: the suturing of the defect is indicated. The definition of gynecological tactics should go parallel to the surgical one immediately, as soon as the assumption of possible endometriosis appeared.Conclusion. It is important to remember about endometriosis of the diaphragm as a possible reason of spontaneous pneumothorax in women of reproductive age. When performing thoracoscopy, a revision of the diaphragm is necessary to identify its possible fenestration. Prevention of recurrent pneumothorax consists in the induction of pleurodesis and the subsequent treatment of endometriosis by an obstetrician-gynecologist.