Acute appendicitis in children is one of the most common diseases requiring surgical treatment and ranks first among all emergency surgeries on the abdominal organs. The incidence of acute appendicitis complicated by peritonitis remains at the same level and does not tend to decrease. The course of the postoperative period in children is of particular interest due to the fact that the child’s body behaves atypically and it is very difficult to predict what complications will follow the operation within the framework of the underlying disease. The article presents a clinical case of successful treatment of peritonitis complicated by bilateral epididymitis. On the second day from the onset of the disease, the patient was hospitalized in the Children’s Clinical Hospital (St. Petersburg) with a clinical picture of acute appendicitis, peritonitis. Surgical treatment was performed: laparotomy, urgent appendectomy after 40/2 hours. Sanitation of the abdominal cavity. On the 5th day after the operation, pronounced scrotal edema appeared on both sides, the condition was assessed as secondary orchiepididymitis. On the 7th day after the surgical treatment, a decision was made to perform bilateral scrototomy. Thus, the clinical observation demonstrates variants of late complications after surgical treatment of purulent peritonitis in children against the background of undiagnosed non-closure of the vaginal processes of the peritoneum on both sides, as well as the possibility of successful complex treatment of such patients in a specialized institution. It is necessary to take into account the need for early diagnosis and planned surgical treatment of testicular hydrocele, including due to the possibility of such complications. Literature data with similar clinical cases are presented in isolated publications.