One of the frequent complications of acute appendicitis is appendiceal mass (AM). This research aimed to specify the criteria of AM diagnostics and determine the rational treatment strategy. It was stated that the duration of disease more than 3 days in combination with palpable infiltrate in the right iliac region and absence of positive appendiceal signs allowed formation of the clinical diagnosis of dense AM and definition of the following diagnostics program. An application of ultrasound study gave the possibility to differentiate AM according to maturity into loose and dense cases. Сomputer tomography and irrigoscopy were used routinely in controversial сases of differential diagnostics of dense AM and oncological diseases of the right areas of the large intestine. Diagnostic laparoscopy should be rational in patients with uncertain clinical findings during dynamic monitoring of imaging of inflammatory infiltrate in the right iliac region and it could facilitate to assess of the possibility of its safe separation. The application of given method of dia gnostics algorithm determined the treatment strategy: laparoscopic appendectomy in case of loose AM and conservative therapy in case of dense AM.