Which shows have basically been in syndication since they first started airing and have never stopped being shown? Off the top of my head I figure there is:

The Simpsons

Married with Children

Full House

Family Matters

Seinfeld

Friends

Star Trek 60's

Saved by the Bell

Gunsmoke

Happy Days?

Law and Order: SVU

I believe it's been in syndication for well over a decade and it's still airing repeats right now on USA and a few other channels.

It's been some years ago, but I recall hearing this: at any given moment, Gilligan's Island is playing somewhere in the world.

Of the ones mentioned by the OP, Simpsons is the only one that I can say has "always" played on one channel or another either FX or, now, FXX). I've never sought out the others, but I would say there are extended periods of times when they did not play (around here anyway).

I guess I would ask "what is your standard?"

DJariya picked a good one with L&O:SVU.

Is Family Matters in syndication still? I honestly don't think I've seen an episode in years.

The various Law & Order shows are constantly on (not just Special Victims Unit but the original is on TNT a lot and Criminal Intent is on USA though not as frequently) as are things like the CSI and NCIS shows. Star Trek and Star Trek: The Next Generation seem to be on the air someplace throughout the years. Batman (66) has aired seemingly since I was a kid on some network. The Simpsons is definitely a big one too. Also classic sitcoms like The Brady Bunch, Gilligan's Island, Full House, Happy Days, Cheers, Seinfeld, etc. seem to be around consistently.

The Big Bang Theory.

Mash, cheers. I see King of of queens since it began, modern family are newer ones that have be continuous for a few years...

ER? Although I haven't seen it on any stations in my area for sometime.

I remember reading about shows that vanished when they went off the air. Happy Days was the example. It had become so unpopular that no one picked it up for syndication. It wasn't rebroadcast for years.

The shows that seem to have been repeated nonstop for fifty years are I Love Lucy, Gilligan's Island, and Perry Mason. I think MASH has been in nonstop syndication since the middle of the the original run.

I Love Luc, Leave It To Beaver

With all the cable tv stations nowadays, most popular modern shows likely won't leave syndication any time soon.

Beverly Hillbillies
Dick Van Dyke Show
Bewitched(color episodes only)
I Dream of Jeannie(color episodes only)
Andy Griffith Show(seasons 1-5)
Bonanza(seasons 1-6)
seasons 7-11 of Gunsmoke were never syndicated. 1-6 went out of syndication in 60s.
The b/w Gilligan's Island were not included in original syndication
Wild, Wild West has been in syndication non-stop. All episodes were syndicated but most local stations did not show the b/w ones. Fans would advertise in the fan club newsletter for b/w episodes they were looking for.

TV Land has been showing the color episodes of the Andy Griffith show weekday mornings.

Many of the older shows have come back into syndication from the alternate digital channels offered by the main broadcast networks. Most of the ones named in this thread play right now, though they had disappeared for a few years before the digital switch-over. One such channel recently picked up the 60's sitcom "The Ghost & Mrs. Muir," which has been a real treat to discover in the past year. It's nothing much like the movie but has its own charm.

Seinfeld, Simpsons and possibly I Love Lucy are just about the only shows to remain in continuous syndication since going off the air on core broadcast/cable channels. Lucille Ball made an absolute fortune off the syndication rights to the show. MASH stayed in syndication for many years but fell off the map for a few years in the last decade.

The amount of money Jerry Seinfeld and Larry David have made from Seinfeld must be mind boggling. I don't blame Jerry for never doing another major project since the show ended. Nothing could ever top it.

They are syndicated separately from the b/w ones.

I always felt that MASH is the cream of the crop in syndication.

I can also watch Seinfeld over and over.

I wonder what the long term outlook is like now that we have Netflix. Is Netflix paying comparable amounts to run shows? The best shows on there (30 Rock, Arrested Development, Family Guy, etc.) still always appear in the "trending" section almost daily. So there must be a lot of people watching.

I see all of these still showing up regularly...

Happy Days
Laverne & Shirley
Three's Company
The Jeffersons
Andy Griffith
WKRP
Barney Miller

For some reason, I haven't seen the Cosby Show lately....

Basically, any show which started airing in syndication either when it was still on the air or after the show was cancelled and has consistently been airing in syndication without being taken off the air. So a show like Full House would count because you could always find reruns of it anytime you wanted , whereas Step By Step wouldn't because it stopped airing for a couple of years came back and disappeared again.

Yes it still is unless it got removed recently. It went from ABC Family/Freeform to BET and now it's on Centric.

I also forgot to add MacGyver would be another show that's been in syndication forever.

I ask about the standard because local channels may not necessarily run the same syndicated shows as other locals, even if they are the same network. Hence, maybe my area doesn't have Gilligan's Island, but my brother does in another city. Of course, the proliferation of cable channels changed things.

Check out the Wikipedia article on "Broadcast Syndication." It doesn't answer the question, but it's pretty interesting!

WKRP is well known for not being in constant syndication. The very first broadcast syndication had all the music intact. After the syndication expired the show was gone for a few years, then resyndicated with replacement music.

That's interesting. What's the reason why they are separate?

My guess is the five b/w seasons were syndicated when the show went color. Went the show finished it's run the remaining color episodes were syndicated in a separate package. The stations airing the b/w ones may or may not have picked up the second package.
Here in Kansas City a local channel still has rights to the b/w episodes. MeTV has to substitute a color episode locally whenever a b/w one is on the schedule.

The b/w episodes of Bewitched and I Dream of Jeannie were never syndicated. Broadcast stations aired the color episodes over and over for 20+ years.
In the early 90s Nick-At-Nite got rights to the "not seen in 30 years" b/w ones. But that is all they had. WGN, TBS and other broadcast stations continued to show only the colors, while Nick showed only the b/w. All episodes have since joined in one package.

Bonanza wasn't syndicated until the show had run it's course. 14 seasons. NBC or Paramount had to decide what to do with them all. They decided to syndicate the first six seasons plus a few from 7 with big guest stars to get a nice round number.
In the mid/late eighties, with cable in full swing, they cracked the vault and syndicated the remaining seasons to either FAM or Hallmark. So the syndication was split.

A few years back, ION aired reruns of ER. I kind of miss that show in syndication.

The replacement music makes it vastly inferior to the original run.