Hereditary fibrinogen amyloidosis is characterized by deposition of amyloid fibrils in renal glomeruli. The subunit protein of the amyloid fibrils is a proteolytic fragment of the fibrinogen Aalpha-chain. To investigate the structure of fibrinogen amyloid, fibrils were extracted from the tissues of a patient and studied by X-ray fiber diffraction and electron microscopy. We have carried out a full structural characterization of amyloid fibrils taken from disease tissue. These studies revealed that ex vivo fibrinogen amyloid fibrils have a cross-beta structure similar to other chemical types of amyloid fibrils.