In my overrated shows thread, someone is claiming that The Honeymooners is not a sitcom but a series of sketches because it only made 39 episodes and the creators ran out of ideas. This thread is to show all the sitcoms that were not as long-running and aired 39 or less new episodes.

The Honeymooners (39)
Fawlty Towers (12)
DAG (17)
Back to You (17)
The Ropers (28)
Raising Dad (22)
Life with Lucy (14)
Ladies' Man (1980) (13)
Ladies Man (1999) (30)
Laurie Hill (9)
Law and Disorder (UK) (6)
Leap of Faith (6)
The Legacy of Reginald Perrin (7)
Life on a Stick (13)
Listen Up (22)
Living with Fran (26)
Lotsa Luck (22)
Love and Money (13)
Love on a Rooftop (30)
E/R (1984) (22)
Enlisted (13)
Encore! Encore! (13)
Eastbound and Down (29)
18 to Life (25)
The Ellen Burstyn Show (13)
The Ellen Show (2001) (18)
Emeril (10)
Emily's Reasons Why Not- this sitcom from 2006 got a lot of promotion but was cancelled after just one episode.
Welcome to New York (16)
Welcome to Sweden (20)
Welcome to The Captain (5)
Better with You (22)
Bette (17)
The Betty White Show (1977) (14)
Bridget Loves Bernie (24)
The Brady Brides (10)

And this is just a small portion of under 40 sitcoms.