The decision to treat a nontraumatic spontaneous pneumothorax with aspiration by catheter, tube thoracostomy, or observation is based on the mechanism, underlying disease, and complicating factors. Any patient requiring general anesthesia or mechanical ventilation should have a tube thoracostomy. Aspiration by catheter may be successful in selected patients, but they should be watched for a period of time with repeat x-rays before being discharged. The possibility of the occurrence of a tension pneumothorax in association with any simple pneumothorax must be kept in mind. Most traumatic pneumothoraces require thoracostomy.