Senile systemic amyloidosis is a common age-related amyloidosis that involves accumulation of wild-type transthyretin, with cardiac dysfunction being a predominant result. The importance of obtaining an accurate diagnosis of senile systemic amyloidosis has been increasingly recognized, so that novel treatments are being developed. However, the clinicopathological features of senile systemic amyloidosis remain to be completely understood. Here, we evaluated cardiac specimens from 181 consecutive post-mortem cases older than 40 years, including 6 cases of senile systemic amyloidosis, and 5 cases of familial amyloidotic polyneuropathy, which is a hereditary systemic amyloidosis caused by mutant forms of transthyretin. Furthermore, we studied ante-mortem clinicopathological findings of 11 senile systemic amyloidosis cases, in which 9 cases underwent gastrointestinal tract biopsy and/or subcutaneous tissue biopsy, at Kumamoto University Hospital. Of the autopsied cases of elderly Japanese (older than 80 years), 12% had senile systemic amyloidosis, with the percentage increasing with age. The occurrence of senile systemic amyloidosis in elderly Japanese patients was lower than that in previous reports, which suggests that a genetic background and/or environmental factor(s) may have important roles in the occurrence of senile systemic amyloidosis. Transthyretin amyloid deposits in familial amyloidotic polyneuropathy cases developed mainly in the pericardium and the surrounding muscle fascicles, whereas in cases with senile systemic amyloidosis the transthyretin amyloid deposits had a patchy plaque-like shape and developed mainly inside the ventricular wall. Biopsies from senile systemic amyloidosis patients evidenced amyloid deposits in 44% (4/9) of gastrointestinal tract and subcutaneous tissue samples combined. As myocardial biopsy may be dangerous for elderly people, the use of a combination of gastrointestinal tract and subcutaneous tissue biopsies may make diagnosis of senile systemic amyloidosis easier.