Male, 76 year-old patient with a history of total hip arthroplasty who presents with a mass in the iliac fossa with swelling of the thigh and hip pain upon flexion and extension. Complementary ultrasound and computed tomography scan studies show a giant lobulated cystic mass in the left iliac fossa, 7 cm in diameter, near the prosthesis. Cyst formation caused by polyethylene disease after total hip arthroplasty is infrequent. We present a case of large psoas bursitis secondary to the release of polyethylene particles which caused superficial femoral vein compression and thrombosis.