An early morning argument apparently prompted one man to stab another one in the Albany Park neighborhood on the Northwest Side.
The 19-year-old man and a man in his early 40s were arguing about 5:45 a.m. in the 3400 block of West Sunnyside Avenue.
During their dispute, the older man produced a knife and plunged it into the victim's chest, police News Affairs Officer Joshua Purkiss said.
The teen was taken in an unknown condition to Advocate Illinois Masonic Medical Center, and it was not clear what they bickering about, the officer said.
No arrests have been made, Purkiss said.