Revealing mistake: When Sara is shaving her hair in front of the mirror, you can see the "join" between her forehead and the "skull cap" she's wearing under her hair.
Continuity mistake: In the scene where Cameron Diaz and her husband are talking to the doctor in a flashback, her hair repeatedly goes from behind her shoulders to in front. it is especially obvious when at one point she turns towards her husband and her hair completely changes position.
Continuity mistake: At the hospital, after Kate has finished vomiting as a result of her chemo, she is cuddling against Taylor. During their conversation about a dance at the hospital, Kate's hair alternates between being in front of her left ear to being behind it.
Plot hole: Anna's lawsuit was completely unnecessary. Regardless of the parent's wishes, no transplant physician or program would ever accept an unwilling minor as a living donor. All Anna would have had to do is express her refusal.
Factual error: In the scene where Anna visits Campbell for the first time, he looks at her medical records, and in the close up it shows Anna's birth date as 05/16/1990, but in the scene where Kate is showing her mother the scrapbook she's made it contains a picture which shows that Kate's birth date is 08/22/1990, which makes Anna somehow 3 months older than her supposedly elder sister.
Continuity mistake: In the scene towards the end of the film when Sara is quizzing Anna on the stand, Sara's arms alternate between folded in front of her in the shots from the front to hands on hips from the back.