Harold Wayne Lovell had left his Chicago home in 1977 to try to find a construction job and had not been seen since, the Chicago Tribune reported.
But he was found in South Florida after family members contacted the Cook County sheriff's office when it reopened the Gacy case to identify eight long-unidentified victims, the Tribune said.
The sheriff's office this month said technology advances had allowed suitable DNA samples to be collected from the remains of eight unidentified male victims. And Lovell's family members contacted the sheriff's office two weeks ago to submit a genetic profile.
But instead of confirming suspicions he was one of the 33 young men and boys killed by Gacy, who was executed in 1994, the family found through a police booking photo online that he was alive, though sometimes in trouble with police, in South Florida.
Before dawn Tuesday, Lovell got off a Greyhound bus and was embraced by his sister and brother.
"I've gone from having nothing to having all this," Lovell said. "It's awesome."
He said he had left home because of differences with his mother. In Florida, he worked in shipyards, did lawn work and painting, and worked with horses. He said he had gotten into minor trouble with the law.
Lovell said he had returned to Chicago once to try to find his mother but she had died in 2001.
His sister, Theresa Hasselberg, said her brother looks old, but she was glad to have him home.
"After all these years, he's home," she said.