E.I. Sigal, R.G. Khamidullin Thoracoscopy is one of the most informative invasive diagnostic methods for diseases of the chest organs. The minimally invasive nature of the procedure, combined with its broad diagnostic capabilities, allows thoracoscopy to be used for targeted biopsies of the pleura, lymph nodes, mediastinal tumors, and lung tissue. Diagnostic thoracoscopy, thanks to the ability to obtain histological or cytological material, allows for a definitive conclusion about the nature of the pathological process. Indications: 1. Exudative pleurisy of unknown etiology. Most often, pleurisy is caused by tuberculosis, malignant mesothelioma, or dissemination of cancer through the pleura. Diagnostic thoracoscopy is performed to obtain complete biopsy material under visual control. Other methods (cytological examination of pleural effusion, blind biopsy) are much less informative. 2. Lung cancer staging. If metastatic involvement of the mediastinal lymph nodes is suspected, diagnostic thoracoscopy with targeted biopsy allows us to determine the extent of the process and avoid diagnostic thoracotomy. 3. Mediastinal lymphadenopathy. Diagnostic thoracoscopy is indicated for all patients with enlarged mediastinal lymph nodes to determine the etiology of the lesion (lymphogranulomatosis, malignant sarcoidosis, tuberculosis), since only histological and histochemical examination of the affected lymph node allows us to establish a diagnosis. 4. Malignant tumors of the mediastinum. These tumors are inoperable at the time of diagnosis in 90-95% of cases. Diagnostic thoracoscopy in this category of patients allows us not only to establish a morphological diagnosis of the tumor, but also to determine its prevalence, invasion of the mediastinal organs and/or lungs for the subsequent administration of adequate chemotherapy or radiation therapy. 5. Disseminated lung diseases. In the diagnosis of interstitial and disseminated lung diseases, diagnostic thoracoscopy with marginal resection is the most accurate method, allowing for histological verification of the process. Bronchological examination and percutaneous lung puncture are uninformative in these diseases. 6. Pericarditis. Diagnostic thoracoscopy allows for clarification of the etiology of pericarditis and for decompression and drainage of the pericardial cavity. Surgical technique: Diagnostic thoracoscopy is performed under local or general anesthesia. A thoracoscope is inserted into the pleural cavity, and it is used to inspect the pleural cavity. If effusion is present, it is aspirated. Pleural diseases. In pleural diseases (malignant mesothelioma, disseminated cancer, tuberculous pleurisy, etc.), up to 20 biopsies are obtained from the most altered areas using biopsy forceps for urgent histological examination. If a malignant process is present, pleurodesis with talc or bleomycin is indicated to obliterate the pleural cavity and stop exudation. If tuberculosis or inflammatory pleurisy is detected, appropriate treatment is prescribed. Lung cancer staging is performed. A biopsy of the mediastinal lymph nodes is performed; if metastases are present, their invasion into surrounding tissue is determined. The biopsy is performed using special forceps or by excision. Minor bleeding from the lymph node is stopped with electrocoagulation. Biopsy of malignant mediastinal tumors is performed using the same technique (Fig. 1). Mediastinal lymphadenopathy. A lymph node biopsy is performed by enucleating it from the surrounding tissue. Care must be taken when isolating the lymph node to avoid damaging it (Fig. 2). Prior clipping of the vascular pedicle is advisable; electrocoagulation is also possible. Interstitial lung diseases. Marginal resection is performed with preliminary application of an endoloop or using a stapler. Pericarditis. Resection is performed using a stapler or scissors. The resected tissue area (pericardial window) should be 2 x 4 cm in size. During the operation, it is necessary to identify the phrenic nerve and adjacent vessels to avoid damaging them. Pericardial effusion is aspirated. The operation is completed with lung inflation, debridement, and drainage of the pleural cavity.