The purpose of this study was to evaluate the clinical and pathological features in patients with progressive-type familial amyloidotic polyneuropathy (FAP) using autopsy and biopsy specimens. A proband is a 33-year-old man with FAP type I who developed motor, sensory and autonomic impairments with neuropathy, heart failure, and anorexia. Genetic findings of transthyretin (TTR) revealed G to A transition in codon 54 causing a rare mutation of TTR Lys54. He died of pneumonia and severe cardiac failure 4 years after onset. Autopsy showed heavy amyloid deposition in the heart, peripheral nerves, thyroid, skin, fat tissue, prostate and testis, moderate in the sympathetic nerve trunk, vagal nerve, celiac plexus, pelvic plexus, bladder, gastrointestinal tract, tongue, pancreas, lung, pituitary, blood vessel, gall bladder, adrenals and muscles, and free in the central nervous system, liver, kidney and spleen. Sural nerve biopsy in a sibling confirmed TTR amyloidosis immunohistochemically. Electronmicroscopic findings of amyloid fibrils were similar to that of FAP Met30. Immunoelectronmicroscopic findings indicated the relationship between amyloid fibrils or non-fibrillar structure and collagen fibers. The distribution of amyloid deposition, heavy in the heart and lacking in the kidney, is a characteristic feature and reflected severity of FAP with TTR Lys54.