Although the entire Wilkerson family is the main cast, the only characters to appear in every episode are Reese, Hal and Dewey. Lois made infrequent appearances during season 4, she didn't appear at all in clip show with the exception of flashbacks. Francis began making infrequent appearances during season 6 and 7, while Malcolm didn't appear at all in clip show 2 with the exception of flashbacks, while Jamie didn't join the series until the season finale of season four.
- The only episode Malcolm didn't appear in was Clip Show #2, where the entire episode focused on Hal and Lois and Malcolm only appeared in flashbacks. Dewey was also seen at the end of the episode and Reese made a brief appearance at the end also.
- Lois didn't appear in the episode Clip Show, where she was only seen in flashbacks. The entire episode focused on Malcolm, Dewey, and Reese and Hal was only seen at the beginning and end of the episode.
- In the episode Boys At Ranch, The male members of The Wilkerson Family went to go and visit Francis at the Cattle Ranch. Lois was not seen in the episode, but she was mentioned by Malcolm, saying that he's going to miss his girlfriend, Nicki, but it'll be great to be rid of mom for a few days.
- For a short period of time is season 4, Lois was absent from the episodes. The reason given was because she was pregnant and decided to live at her sister's house for a short period of time. The first episode without her was Kicked Out and she was also absent in the episodes Stereo Store and Hal's Friend. It wasn't until the episode Garage Sale that she made her return.
- Francis has made the most amount of absences out of all of them, having only appeared in a couple episodes of seasons 6 and 7.