The aim of this study was presenting significance of diagnostic process in doctor’s daily routine. A 45-year-old patient for a planned laparotomy due to left ovarian cyst detected with a routine transvaginal ultrasound. She did not report any symptoms. Computer tomography of the abdomen and pelvis showed a cystic lesion with segmental wall thickening, measuring 133 x 83 x 135 mm, adjacent to the left ovary and the uterus on the left side. At the laparotomy exploration, a giant cyst, ca. 20 cm in diameter was found above the uterus, on the left side, in the area between the lower and middle abdomen. The histological exam results showed lymphangioma of the small and large intestine mesentery. In this case, lymphangioma was found in a rare location, in the mesentery of the ileocecal valve. It did not present any signs and symptoms. CT used in the present case failed to identify the exact point of origin of the lesion.