AN OAK LANE woman fatally shot a man who had pistol-whipped her son while trying to rob him last night, police said.

Police responded to the Adams Run apartment complex, on Godfrey Avenue near Crescentville Road, about 9:15 p.m., and found a 19-year-old man shot once in his chest at the bottom of the stairs near a basement, police said. He was pronounced dead at 9:24 p.m., with his gun beside his body.

The 43-year-old woman, who was not identified, called 9-1-1, saying that she had shot a man who repeatedly hit her son over the head with a gun, Police Inspector Scott Small said.

"She was intervening in a robbery and had to use deadly force," Small told reporters at the scene last night.

Her son was taken to Albert Einstein Medical Center to be treated for graze wounds to his head.

Cops said that the man's mother and his 23-year-old girlfriend were both in custody.

Small said that the mother had a permit to carry a firearm.

No charges were filed as of late last night.