Nearly 200 centenarians in Japan are missing, according to a national audit.
The inquiry followed the discovery last month of the mummified remains of a man registered as being 111 years old.
Among those missing are 21 people who would be older than the nation's current official oldest person of 113.
There are more than 40,000 centenarians in Japan, according to government data, but the number of missing has raised concerns that the welfare system is being exploited by dishonest relatives.
Sogen Kato was thought to be the oldest man in Tokyo - but when officials went to congratulate him on his 111th birthday, they found his 30-year-old remains.
He had received about 9.5m yen ($109,000; £70,000) in pension payments since his wife's death six years ago, and some of the money had been withdrawn, reports said.
Police are now investigating his family on possible fraud charges.
Just days later officials discovered that Tokyo's reputed oldest woman had been missing for decades.
At least 38 of Japan's 47 prefectures have started checking the whereabouts of people 100 years or older, Japan Today reported.
Those unaccounted for include a 125-year-old woman whose registered address was turned into a park in 1981, the newspaper reported.
Japan has one of the world's fastest ageing societies, with one in five over the age of 65.
In the last 10 years the number of centenarians has more than tripled to 40,399 - 87% of whom are women, according to the latest government figures.
But the discoveries have cast doubt on the accuracy of the numbers.