The authors report an unusual complication of total hip arthroplasty. A patient developed significant swelling and discomfort in the left lower extremity 4 1/2 years following a left total hip arthroplasty. Magnetic resonance imaging and venography demonstrated a large intrapelvic mass compressing the external iliac vein. An arthrogram revealed a cystic cavity consistent with an iliopsoas bursa in communication with the hip pseudocapsule. Two aspirations of the bursa led to resolution of the cystic enlargement and symptoms. An enlarged iliopsoas bursa should be considered in the differential diagnosis of hip pain or extremity swelling after total hip arthroplasty.