It was only when the postman began having trouble pushing post though the letter box that suspicions were aroused, according to local newspaper Smålands-Tidning.
On Monday morning the postman informed the police.
With assistance from the property owner, police were able to gain access to the apartment were they found the man, who was in his sixties, dead.
Police estimate that the man could have lain dead for up to a year.
Forserum is a small society of 1,982 inhabitants in the Swedish countryside near Jönkoping. It is as yet unclear why the man was able to go unnoticed for such a long period of time.
A neighbour told the newspaper that officers from the Swedish enforcement service (Kronofogden) had been knocking on the man’s door since the autumn.
It is known that the man had spent periods living at another address although his car had been parked outside the building in its normal place, a factor which would be expected to gain the attention of the landlord.
Police have conducted a forensic examination of the apartment and report that there is currently no suspicion of any criminal offence.