Perforated peptic ulcers are frequently sealed spontaneously by omentum or by adjacent organs, and the associated peritonitis resolves without operation. Several surgeons, nearly 40 years ago, have applied their knowledge of the phenomenon of spontaneous seal to the treatment of the perforated duodenal ulcer and their reported mortality rate was almost half that generally recorded mortality rate for surgical treatment at that time. But despite these encouraging reports of successful non-op treatment of the perforated duodenal ulcer, the conservative treatment had not been gained widespread acceptance. Instead, much of the recent surgical literature concerns not whether patients with perforated duodenal ulcers should have an operation, but whether a definitive operation to heal the ulcer should be performed at the time of perforation. But recently there was a significant advances in ulcer treatment and antibiotic therapy. And also there was a few promising reports of non-op treatment of the perforated peptic ulcers by means of a prospective randomized or selective trial. In this study, we compared the clinical charateristics of emergency operative treatment group with non-op group retrospectively to offer the opportunity to reap- praise the role of the non-op treatment of the perforated duodenal ulcer. Our data suggest that perforated duodenal ulcer can be safely treated non-op when spontaneous seal of the ulcer perforation had occured. Therefore, efforts to induct and maintain the spontaneous sealing by using the initial observation period should be made positively.