Cartman's Mom Is a Dirty Slut is the 13th episode of South Park which aired on February 25, 1998. It is part one of a two episode story arc, which concluded with "Cartman's Mom Is Still a Dirty Slut".
In the recent UK poll Paramount Comedy's Top 10 Episodes, this episode was ranked number 10.
In a classic cliffhanger, Cartman needs to find out who his father is but his mom is no help. Learning that his father could be one of the many people that his mom "had relations" with during an annual party called "The Drunken Barn Dance", he finds that there's more to his mother than he thought.
Based on everyone's best recollections of the time, Mrs. Cartman had met Chief Running Waters, followed by Chef. She briefly becomes infatuated with the 1989 Denver Broncos before Mr. Garrison appeared. As the story unfolds, Cartman visits Running Waters, Chef, and Mr. Garrison and questions them about being his father, but it becomes too apparent that visiting each potential father individually is a lost cause when he questions Mr. Garrison. Mr. Garrison admits that he'd slept with Mrs. Cartman, but then argues "but who the hell hasn't!?" (to which Mayor McDaniels, Principal Victoria, Jesus and Father Maxi share guilty glances with each other). Dr. Mephisto is willing to perform DNA testing to resolve the issue, but requires $3,000 for the test. In the meantime, Kyle, Kenny, and Stan videotape Cartman having a tea party in his backyard with stuffed animals. They come up with the idea to send the video into America's Stupidest Home Videos for the chance to win $10,000. Cartman then approaches Kyle and Stan (since Kenny was killed by a train) with the depressing news about his lack of funds to find out his real father. Stan and Kyle agree that if they win the video contest they will give Cartman the $3,000 needed for the DNA testing. Cartman is overjoyed, but quickly becomes extremely pissed off after seeing the aired video. However, the tape loses to Grandpa's tape of Kenny's death, so they get a $3,000 runner-up prize instead, which all goes to Cartman.
After the DNA testing, candidates for the identity of Cartman's father are limited to Officer Barbrady, Chef, Jimbo, Ned, Mr. Garrison, Chief Running Waters, Gerald Broflovski (Kyle's father, with the possibility of Cartman being his half-brother upsetting Kyle), Dr. Mephisto, Kevin, and the Denver Broncos. The narrator concludes the episode with a cliffhanging question "Who is Eric Cartman's father?"
The story was continued in "Cartman's Mom is Still a Dirty Slut".