In the episode, 'Karate Kid', Wilson says that he wrote the book 'The Psychophysiological Indices of Amorous Connections Among Termites of the Southwest'. In the episode 'Wilson's Girlfriend', that book was given as the title of Jill's psychology professor. However, in both episodes, it had only managed to sell 4 copies.
Despite the character of Al being single for much of the series, Richard Karn always wore a wedding ring on the show (because he is married in real life).
Al's girlfriend, Ilene is first introduced as Ilene Markum. But in 'Dream On' the credits says that her character is Ilene Martin.
Tim only has four brothers but a total of six different men have been named as Tim's brothers. Jeff and Marty we've met the others named are Danny, Brian, Rick and John.