Sixty-nine patients with a Greenfield inferior vena cava (IVC) filter in place for 1-9 years were evaluated with supine abdominal radiographs. In 22 patients (32%) the filter span diameter had increased by 3-11 mm, and in six patients (9%) it had decreased by 3-18 mm. Twenty patients (29%) had caudad migration of 3-18 mm, and four (6%) had cephalad migration. In five patients (7%) the filter was at an angle of more than 16 degrees from the vertical. A decrease in filter span of 7 mm or more may result in IVC occlusion, whereas an increase of 6 mm or more may result in caval wall penetration. Caudad migration may be caused by a fibrous reaction around the struts which slowly draws the filter caudally. A change in filter angle may result from displacement of a strut into the right renal vein as well as from physiologic changes. The abdominal radiograph is a valuable method for follow-up study of patients with Greenfield filters if the filter position, span, migration, and angle are noted in the report.