Spontaneous pneumothorax has been managed on an outpatient basis by intercostal tube drainage and a portable flutter valve device (pneumothorax set). In a series of 111 selected patients, from 14 to 75 years of age, who had no complaints such as dyspnea, had neither tension-nor hemo-pneumothorax, and could promptly return to hospital in an emergency, intercostal tube insertion and continuous negative pressure drainage were instituted at the outpatient department. After approximately one hour of suction, if an air leak ceased and the lung was re-expanded, the patient was allowed to return home with a pneumothorax set connected to the chest tube. But, if an air leak persisted, they were admitted to hospital. The outpatients were followed every 2 or 3 days thereafter, and if their course was uneventful, the chest tube was removed a week later. If the onset of lung recollapse was seen at outpatient check up, hospitalization was required. Outpatient treatment was successful in 81 cases (72.9%) of the series. However, 14 patients were hospitalized because of persistent air leak at the outpatient room, and 5 were admitted because of wound pain, re-expansion edema or other reasons. During the ambulatory course, 11 were admitted to hospital with recollapse of the lung. Bacterial cultures of drain tips were positive in 22.6% of 75 examined cases, which was a higher percentage than that associated with inpatient drainage. Wound infection with St. aureus occurred in one case after removal of the drain.(ABSTRACT TRUNCATED AT 250 WORDS)