The body was discovered inside a home in Hermiston Road, Sprinboig, in the east of Glasgow, at around 10am yesterday.
Officers cordoned off a large area of the street, from Glen Avenue to Threestonehill Avenue.
The park next to a burn beside the property was taped off and an incident tent was set up on a path beside Hollowglen Road.
Several streets away on Tynecastle Street, an officer was standing guard at a phone box and hedge which had police tape around it.
It is understood the cordon was connected to the death, which police confirmed was being treated as suspicious.
A forensic team was at the scene examining evidence.
The area is home to elderly people and families. A man, 72, who lives on Hermiston Road, said: "There's never any trouble here and I didn't hear anything last night or this morning. When I came back from swimming at 12pm there were five police cars and police tape everywhere on the street. It's a very quiet area but there are a few drugs problems in some of the flats."
A Police Scotland spokeswoman said: "The body of a man was found within a flat in Hermiston Road, Glasgow, at about 10am. Inquiries are ongoing.
"At this time the death is being treated as suspicious. A post mortem will take place in due course."