This is a list of notable events, premieres, releases, series cancellations and endings, and other business ventures for Nickelodeon in the year 1991.
- March 18 - Get the Picture
- March 23 - Clarissa Explains It All
- June 1 - Salute Your Shorts
- August 11 - Doug, Rugrats and The Ren & Stimpy Show (the first three Nicktoons)
- August 31 - What Would You Do?
- September 6 - Launch Box
- October 31 - Are You Afraid of the Dark? airs its pilot episode
- June 6 - Hey Dude season five
- August 30 - Hey Dude, five seasons
- December 6 - Get the Picture, two seasons
Nickelodeon character debuts
- Clarissa Explains It All: Clarissa Darling
- Doug: Doug Funnie, Porkchop, Skeeter Valentine, Patti Mayonnaise, Roger Klotz
- Rugrats: Tommy Pickles, Phil and Lil Deville, Chuckie Finster, Angelica Pickles
- The Ren & Stimpy Show: Ren Hoek, Stimpy J. Cat, Mr. Horse, Muddy Mudskipper, The Fire Chief
Behind the scenes
- Nickelodeon places its first renewal order for additional episodes of all three Nicktoons (26 more each for Doug and Rugrats, and 20 more for Ren & Stimpy).