The man, who is reported by the Aftonbladet daily to have been born in 1928, was found when a broadband technician turned up to complete an installation in the building and found the apartment door unlocked.
"Two men went into the apartment and found the man dead. They called me and we discovered that we had lain there a while," project leader Thomas Martinsson told the newspaper.
"It is very tragic," Åsa Johannesson at Flemingsberg police said.
Exactly when the man died can not be established for certain but police found unopened mail from late 2007 and the food in the fridge was dated early 2008.
Furthermore the man's advanced state of decay indicated that he had been dead for around three years.
The man's pension had continued to be deposited to his account and his bills had been paid by direct debit throughout the time he lay dead in his apartment.
The man is reported to have relatives and police are trying to get in touch with his next of kin, a son.
"He lived alone but there are relatives. But they obviously had no contact," Åsa Johannesson said.
The police have confirmed that there is no suspicion of any crime having been committed.