The victim was found dead in his apartment in the 400 block of Valencia Street at 11:55 a.m., Lt. Troy Dangerfield said.
The man was identified today by the medical examiner's office as 32-year-old Oliver Carter.
Homicide investigators are not discussing how Carter died, but a suspect in the case was arrested Monday, Dangerfield said.
The suspect, James Warren, 53, of San Francisco, was booked into jail on suspicion of murder, Dangerfield said. Warren's relationship to Carter was also not released.
The death is San Francisco's 48th homicide this year, according to police.