Police say 59-year-old James Benson walked into Hutcheson Medical Center in Georgia where his wife, 56-year-old Mary Benson, and her mother, 76-year-old Charlotte Johnson, were visiting a sick relative in the intensive care unit.
Witnesses said James Benson got into a brief exchange with his wife and Johnson. Authorities said he told them "they'd be sorry," walked to his car and returned with a gun, fatally shooting both victims.
"He shot the mother-in-law-first and then shot his wife," said Fort Oglethorpe Police Chief David Eubanks. "There was a crowd of the folks in the waiting room, but he just exacted his revenge on his two targets and left them alone."
Investigators say he drove to the police station and turned himself in shortly afterward.
Police say the suspect's marital problems apparently prompted the shooting. They say he will be charged with two counts of murder, and that other felony charges are also likely.
The Associated Press contributed to this story.