The man was found unconscious and unresponsive at the corner of 19th and Folsom streets at about 4:15 a.m., according to police and the medical examiner's office.
The medical examiner's office said this morning that the man's death was consistent with a hit-and-run involving a vehicle, but a conclusive determination has not been made.
The man's name is being withheld pending notification of his family. He appeared to have no fixed address, according to the medical examiner's office.