I have all of the seasons of SG-1 and most of Atlantis and have been watching SG-1 from the beginning, currently up to Season 6 I believe. What I'm wondering is at what point do I need to start watching Atlantis? Does it start after SG-1 ends or do I need to be watching them simultaneously at some point? If so, where do I pick up Atlantis at?

I never watched SG-1, but own the complete series set and intend to watch it at some point.

I watched probably 90% of Atlantis' run (missed most of the final season)

I'm not sure when, but a few characters from Atlantis are initially introduced in SG-1.

Atlantis and SG-1 ran simultaneously for a couple of seasons. The plots are totally separate. I believe Richard Dean Anderson was in Atlantis' Pilot to help launch and made an occasionally guest appearance here and there. But, you can safely watch Atlantis after you finish SG-1 without any worries.

Atlantis premiered with the eighth season of SG-1, no major crossovers, just a few characters showing up on the other show a couple of times. I'd watch them concurrently from season 8 since you have both shows.

Ok, thanks a lot guys!

There was one major crossover. An early SG-1 season 10 episode where the SG-1 crew went to Atlantis to complete a mission. However, it was a character only crossover, there was no major plot crossover. SG-1 basically took their plot and crew to Atlantis, mingled a little, did there thing and went home.

However, even though there is virtually no contact between the two shows for seasons eight/one I would recommend mixing it up between them. R.D. Anderson significantly cut back his time on the set in season 8, and it showed on the screen with a noticeably disjointed season. Atlantis on the other hand recaptured some of the feel of the earlier SG-1 seasons.