Continuity mistake: On the video of Ian supposedly killing Alison, we see her arm fall to the ground with her "Alison" bracelet visible. But in a later scene where Emily watches Ian put his bag in the athletics room, we cut back to the video and Alison's arm suddenly has a sleeve covering up her bracelet. When we see the video again later in the series, her bracelet is visible again.
Careful What U Wish 4 - S1-E14
Other mistake: During the scene after the fund raising dance when Lucas offers to take Hanna home, she calls him Ian when she says that she is going home with Emily and Spencer. Even if she says "I kind of promised them", the subtitles say Ian.
Someone to Watch Over Me - S1-E20
Continuity mistake: After Jenna is slapped by Hanna in the bathroom a single tear streams down her right cheek. The next shot of Jenna shows the tear track on her left cheek.
Continuity mistake: When Aria's dad drops her off at school, the camera angle out the passenger window shows her wearing blue jeans. Once she's out, the camera angle changes and she's wearing black Levis.
If at First You Don't Succeed, Lie, Lie Again - S1-E15
Continuity mistake: When Spencer and Emily are done eating pizza, Spencer stacks both their plates. However, when Emily storms off, the plates are unstacked again and now there is a napkin on her plate.
Continuity mistake: In the scene when Ezra rides up behind Aria in the Limo, you can see his hand up to his head, as if on the phone. The camera then cuts to Ezra in the Limo and you see him answer his phone. (00:22:25)
Factual error: Emily is supposed to meet Paige at a karaoke bar at the intersection of 202 and W. Chester Pike, however this intersection is actually an overpass. 202 crosses over top of West Chester Pike, but never actually intersects it.
