“This is a type of abandonment, through disinterest,” said Hiroshi Takahashi, a professor at the International University of Health and Welfare in Tokyo. “Now we see the reality of aging in a more urbanized society where communal bonds are deteriorating.”

Officials here tend to play down the psychosocial explanations. While some older people may have simply moved into care facilities, they say, there is a growing suspicion that, as in the case of the mummified corpse, many may already have died.

Officials in the Adachi ward of Tokyo, where the body was found, said they grew suspicious after trying to pay a visit to the man, Sogen Kato. (They were visiting him because the man previously thought to be Tokyo’s oldest had died and they wished to congratulate Mr. Kato on his new status.)

They said his daughter gave conflicting excuses, saying at first that he did not want to meet them, and then that he was elsewhere in Japan giving Buddhist sermons. The police moved in after a granddaughter, who also shared the house, admitted that Mr. Kato had not emerged from his bedroom since about 1978.

In a more typical case that took place just blocks from the Mr. Kato’s house, relatives of a man listed as 103 years old said he had left home 38 years ago and never returned. The man’s son, now 73, told officials that he continued to collect his father’s pension “in case he returned one day.”

“No one really suspects foul play in these cases,” said Manabu Hajikano, director of Adachi’s resident registration section. “But it is still a crime if you fail to report a disappearance or death in order to collect pension money.”

Some health experts say these cases reflect strains in a society that expects children to care for their parents, instead of placing them in care facilities. They point out that longer life spans mean that children are called upon to take care of their elderly parents at a time when the children are reaching their 70s and are possibly in need of care themselves.