Garden Grove police received a call shortly before 2:30 a.m. Sunday of shots fired near Harbor Boulevard and Westminster Avenue.
As officers searched the area, a 19-year-old man who had been shot arrived at a local hospital.
He was immediately pronounced dead by hospital staff.
Officers then discovered a second person who had been shot. That victim was also taken to a hospital and reported in serious but stable condition.
Neither victim has been identified. No suspects have been arrested. Police believe the shootings are gang-related.
Anyone with information that can help the investigation is asked to call the Garden Grove Police Department at (714) 741-5704.