Introduction. Urachal cyst is a congenital malformation, presented by a closed cavity filled with serous fluid in the urachus. Although a morphological picture of the urachal malformation is well known and is quite common in different patients, each case with a complicated cyst has unique clinical features, requiring a differential diagnosis.

Aim. To demonstrate differential diagnosis of two cases with congenital urachal malformations, presenting different clinical features.

Materials and methods. The study describes 2 clinical cases. A 65-year-old patient presented with non-intensive hematuria and fever up to 37.5 ° C, symptoms appeared 2 weeks after blunt abdominal and chest trauma with 7-10th ribs fractured on the left side. Ultrasound revealed a cystic formation of the urachus, up to 6 cm in size. The 2nd patient - 62-year-old with a bladder tumor. MSCT revealed a mass (tumor of the urachus) with signs of invasion into the bladder anterior-superior wall, with signs of involvement in the process of one loop of the small intestine and the proximal part of sigmoid colon.

Results. The first patient underwent an open surgery: partial midline laparotomy with excision of an umbilical hernia, containing a portion of the greater omentum. The 62-year-old patient also underwent an open surgery - lower midline laparotomy with removal of the urachal tumor, bladder upper hemisphere, and a part of the small intestine.

Conclusions. In the first clinical case, the complicated urachal cyst simulated bladder cancer. Visual differential diagnosis of urachal festering cyst with its possible malignant neoplasm directly during the surgery was hampered by secondary tissue changes and other organs involvement. In the second clinical case actinomycosis was identified, which probably provoked inflammatory changes in the urachal cyst. This manifested the clinical picture and required radical surgical treatment.