4.02 - Things I Forgot At Birth
*When Nathan wakes up on the bridge his shirt has the number 20 backwards, but in the episode previous it was the right way when he was on the bridge.

4.03 - Good News For People Who Love Bad News
*In the last scene when we see Derek cutting up Peyton's picture for his wall, the camera shows all of his stalker photos. But in one photo both Derek and Peyton are in it, so he couldn't have taken the photo.

4.09 - Some You Give Away
*In the café, Rachel hands Haley her purse, but when Nathan and Haley walk out of the café, Haley has no purse with her.
*When Deb wakes up in the rehab center, the nurse has turned on Tree Hill's Championship game, but the game actually on TV is an Iowa State Cyclones Basketball game. The logos on the floor are completely different.
*At the end of the episode, the paramedics are doing CPR on Lucus. The paramedic is doing compressions on Lucus's abdomen, instead of his chest to keep his heart pumping.

4.10 - Songs To Love And Die By
*Keith visits Lucas in a dream and shows him what would have been if Lucas was not the guy he is. In the dream, it shows Keith wearing what he wore when he was shot. However, when he was shot, he was wearing a green undershirt, but in the dream, it shows him wearing a white undershirt.
*When the medic is giving Lucas CPR, he is pumping his stomach, not his chest where his heart would be. Pumping his stomach would do nothing in the case of Cardiac arrest.

4.11 - Everything In Its Right Place
*When Lucas is in the graveyard at Keith's and Jimmy's graves, there are two different months printed on the stones.
*After Lucas' heart attack Lucas visits Keith's grave and then visits Jimmy Edwards grave. Jimmy Edwards gravestone shows that they died on March 1, 2006. Not only does that mean that all of season 4 happened in 3 months but when they made the 4 year jump to season 5 it means the show would be in 2010.
*When Nathan comes to apologize to Haley and holds up his hand as he says "always and forever" to show her his wedding ring, Karen sees the bruises on his hand and realizes that Nathan was the one who had punched Daunte, not Dan. However, Nathan had clearly punched Daunte with (and bruised) his right hand, and here he is holding up his left hand which shouldn't have been bruised at all.

4.13 - Pictures Of You
*After Nathan tells Peyton his secret, she tells him her secret, that she can't whistle. However in an episode of Season 2 (Near Wild Heaven) Peyton whistles at Haley to get her to sit up.
*Lucas is at the cemetery visiting Keith's grave. It is clear the date of death is Jan 23, 2006. Lucas then visits Jimmy's grave and his date of death is March 1, 2006. Since Jimmy is the one who "shoots Keith" and then shoots himself, Keith and Jimmy would have died on the same day during the school shooting.
*When Haley is talking to Skills she lies down on a table and the pillow that makes her look pregnant is visible.

4.16 - You Call It Madness, But I Call It Love
*When Derek/Ian ties up Brooke next to Peyton she is able to get the handkerchief off of her mouth. When Brooke says, "Untie me, you freak." you can clearly see the handkerchief around her neck. When it flashes back to Derek/Ian and he says, "Figure's you do good with your mouth." you can see Brooke and the handkerchief is around her chin.
*When Peyton is tied up in her basement by psycho-Derek the night of prom, she tries to call Lucas with her cell phone, but Derek hear the phone ring and take it away from her. When the camera is on the phone, you can see the date on her phone who is 2/1/2007, several months before prom.

4.20 - The Birth And Death Of The Day
*The show is supposed to take place in Tree Hill, but the location on the hospital clearly states New Brunswick County, which is the real filming location of the fictional town of "Tree Hill".
*When Lucas is sitting in the hallway of the hospital, the elevator door opens and Haley, Nathan and Deb walk out of it and see him. While they are talking, it is very obvious that they are on the first floor because you can see the number 1 on the elevator behind them. They would not be coming down from a higher floor to see Lucas if they had just gotten there.

4.21- All Of A Sudden I Miss Everyone
*At the going away party when the girls are dancing to Spice Girls, Haley's shoes switch back and forth between high heels and tennis shoes.