The shooting happened around 3:30 a.m. at the Shell gas station near West Roosevelt Road and South Central Avenue, police said.
"Upon arrival our officer located two gunshot victims that were immediately transported to Mt. Sinai hospital," Cicero Police Department First Deputy Superintendent Luis Gutierrez said. "At that scene, one person was declared deceased, a 23-year-old male, and a second is in critical but stable condition, he's a 28-year-old male."
Officers said the incident started as a verbal altercation and escalated to gunfire.
The shooting remains under investigation, police said. No arrests have been made.
No further information was immediately available.