Continuity mistake: In the episode "Grace, Replaced", with the neighbor Val who moves into "apartment 15F" in the same building as Will and Grace. Yet in the previous episode "Yours, Mine or Ours" with Peter (who moved into 12D) we learn that 12 is the highest floor in the building...
Plot hole: Ellen and Rob wear wedding rings, yet their wedding is not announced until "An Affair to Forget" in the second season.
Continuity mistake: In the poker scene at the beginning of the pilot we witness Will, Jack, Rob, and others playing cards. Shortly after Jack asks for "four cards please" watch the bottom left of the screen as a hand (presumably Will's) deals Jack a single card. In the next shot Will appears to have not dealt Jack any cards yet and when he does he gives Jack five cards, add that to the single card he gave in the previous shot and the Ace Jack kept from his original hand and we get a total of seven cards. Two more than Jack should have had if the hand was dealt correctly.
Continuity mistake: Following the argument between Will and Grace when she returns from City Hall, Karen tells Grace she "thinks it's time for a couple of blue bibbies." Watch closely as she removes the lid from the pill bottle, takes out some pills, and puts the lid back on. The scene shoots to Grace and we hear Karen shaking the closed bottle. When the scene shoots back to Karen we see that the pill bottle is open again and Karen closes it yet again.
Continuity mistake: When Grace has the idea to move into Will's apartment, we can see her cup of coffee on the table. Then a little later during their conversation, the cup moves. (00:23:00)
Continuity mistake: When Karen is sorting out her clothes at her work desk, the black sweater hanging over the desk lamp disappears then reappears. (00:26:40)
Continuity mistake: When eating in Will's office, Grace eats salad from a plastic container. Through the scene the salad in the container changes colour, position etc. Also between shots, lettuce appears on Grace's fork. (00:28:05)
Continuity mistake: After Will pours himself a cup of coffee, he places the coffee jug on the sink desktop. In the next shot the jug is visible on the other worktop, beside the gas cooker. (00:35:50)
Visible crew/equipment: When Karen offers her hand to Jack when they first meet, you can see the boom mike at the top of the shot. (00:37:25)
Continuity mistake: After Karen takes her black top off and throws it down on the table, whilst talking to Jack as they first meet, in following shots the top changes position a few times. (00:37:40)
Continuity mistake: When we first see Grace in her apartment with everything in place, there is a peach coloured chair with a red sheet thrown over it, which changes position in the next shot. (00:39:10)
