It was established from study of the case records of 98 patients that concealed perforating gastroduodenal ulcers take a phasic clinic 1 course. Each phase has a characteristic symptomatology. Special methods of examination increase the possibility of establishing the diagnosis. Concealment of the ulcers is caused predominantly by two main conditions: a small size of the perforation and localization of the ulcerous process on the anterior wall of the pyloroduodenal zone. The larger the perforation, the more probable is the presence of pneumoperitoneum. All patients with concealed perforating gastric and duodenal ulcers must be subjected to emergency operative treatment. The average duration of in-patient treatment depends on the time of hospitalization, timely diagnosis and operative intervention, and the presence of complications. Their prevention is therefore one of the most important problems.