- December 1, 1999
- December 2, 1999
- December 3, 1999
- December 4, 1999
- December 5, 1999 (The last interaction between Linus and Sally)
- December 6, 1999
- December 7, 1999
- December 8, 1999
- December 9, 1999
- December 10, 1999 (This strip is adapted in I Want a Dog for Christmas, Charlie Brown)
- December 11, 1999
- December 12, 1999 (The last interaction between Lucy and Rerun)
- December 13, 1999 (The final appearance of Lucy)
- December 14, 1999 (The day that Charles M. Schulz announced his retirement)
- December 15, 1999
- December 16, 1999
- December 17, 1999
- December 18, 1999
- December 19, 1999 (The inclusion of a detail from Washington Crossing the Delaware in this strip makes it a rare one in which adults appear)
- December 20, 1999
- December 21, 1999 (The final appearance of Spike)
- December 22, 1999
- December 23, 1999
- December 24, 1999
- December 25, 1999
- December 26, 1999
- December 27, 1999
- December 28, 1999 (The last interaction between Sally and Snoopy)
- December 29, 1999 (The final appearance of Snoopy as the World Famous Attorney)
- December 30, 1999 (Rare strip in which the lettering was done by another person due to Charles M. Schulz's failing health)
- December 31, 1999 (Rare strip in which the lettering of the last panel was done by computer due to Charles M. Schulz's failing health)
