This is the fourth update of the guidelines for the diagnosis and treatment of pneumothorax published by the Spanish Society of Pulmonology and Thoracic Surgery (SEPAR). Spontaneous pneumothorax, or the presence of air in the pleural space not caused by injury or medical intervention, is a significant clinical problem. We propose a method for classifying cases into 3 categories: partial, complete, and complete with total lung collapse. This classification, together with a clinical assessment, would provide sufficient information to enable physicians to decide on an approach to treatment. This update introduces simple aspiration in an outpatient setting as a treatment option that has yielded results comparable to conventional drainage in the management of uncomplicated primary spontaneous pneumothorax; this technique is not, as yet, widely used in Spain. For the definitive treatment of primary spontaneous pneumothorax, the technique most often used by thoracic surgeons is video-assisted thoracoscopic bullectomy and pleural abrasion. Hospitalization and conventional tube drainage is recommended for the treatment of secondary spontaneous pneumothorax. This update also has a new section on catamenial pneumothorax, a condition that is probably underdiagnosed. The definitive treatment for a recurring or persistent air leak is usually surgery or the application of talc through the drainage tube when surgery is contraindicated. Our aim in proposing algorithms for the management of pneumothorax in these guidelines was to provide a useful tool for clinicians involved in the diagnosis and treatment of this disease.