An extremely rare case of familial amyloidotic polyneuropathy (FAP) complicated by neuroarthropathy (Charcot joint) in the left knee joint and by intra-articular deposits of amyloid was observed. FAP-specific variant transthyretin (TTR) was found in the synovial fluid and amyloid deposits were confirmed in the synovium, cartilage and bone by Congo red staining and immuno-staining.