Late arterial hemorrhage secondary to a Greenfield filter requiring operative intervention. Retroperitoneal hematomas associated with Greenfield filters have been described and are generally characterized as clinically insignificant. We report a retroperitoneal hematoma that was associated with a Greenfield filter and that required operative intervention because of hemodynamic instability. At operation a lumbar arterial laceration apparently caused by a protruding filter prong was identified and ligated. The implications of this occurrence for filter placement indications are discussed. The potential life-threatening severity of filter-associated hematomas is emphasized. 