Background. Isolated aneurysm of internal iliac artery is very rare and often asymptomatic. Aneurysm itself can produce malfunction of the pelvic organs. Aneurysm rupture is followed by high mortality. Case report. A 76-year old patient was admitted to the hospital with abdominal and left groin pain, disuric problems, obstipation and the signs of intestinal subocclusion. These problems persisted over the last few months. Digitorectal examination showed pulsatile tumor. Computed tomography and angiography revealed isolated aneurysm of the left internal iliac artery with a maximal diametar of 13.5 cm. The aneurysm was treated operatively using extraperitoneal approach in general anesthesia. During the operation a Cell Saver was used. The left internal iliac artery was resected and ligated with end-aneurysmatic suture of its branches. Conclusion. Isolated aneurysm of the internal iliac artery should be considered by differential diagnosis in any case of the occurrence of disorders of the pervic organs functions. Clinical findings, ultrasound examination, computed tomography and angiography are the diagnostic techniques of choice which can confirm the diagnosis. Surgical treatment with the use of retroperitoneal approach lead to complete recovery, so it could be considered the method of choice for patients with the condition permitting a radical surgical approach. .