According to police, the victim was walking home from a friend's house at about 11:50 p.m. when a man who he did not know confronted him near the intersection of Western Avenue and Upham Street.
The suspect pulled out a large fixed-blade bowie-style knife and slashed at the victim, police said.
The suspect then fled the scene.
The injured victim called a friend, who picked him up and drove him to Petaluma Valley Hospital for medical treatment, police said.
Officers responded to the scene of the stabbing, but did not locate the suspect.
Police said the victim described the suspect as a white man, between 18 and 20 years of age. He was wearing a black zip-up sweatshirt with the hood up and a sheath containing a large bowie-style knife at the time of the attack.
After receiving treatment for superficial injuries, the victim was released from the hospital.
Anyone with information about the identity of the suspect or the motive for the attack is urged to contact Petaluma police at (707) 778-4372.