We report a 19-year-old man without a history of primary lung disease or recent trauma presenting with a spontaneous pneumothorax which later developed into a tension pneumothorax. Immediate chest decompression was delayed while awaiting results of chest radiography, despite the patient's rapidly deteriorating condition. His vital signs subsequently became stable after chest decompression. A tension pneumothorax is a clinical emergency that can occur after a spontaneous pneumothorax. It should be suspected in any patient with a spontaneous pneumothorax whose condition deteriorates acutely. Immediate chest decompression should not be delayed.