Continuity: Season 6 - Episode 1 - My Mirror Image: Dr. Cox's hair colour and length change back and forth significantly during the episode.

Continuity: Season 5-9, Episode: My Half-Acre. While Cox and Carla are telling Mrs Wilk about her treatment, the cardigan she is wearing is completely unbuttoned. When the camera goes for a closeup of her face, the cardigan is now buttoned right up to her neck.

Plot hole: Season 5, episode 20 (My Lunch). One of Dr. Cox' patients needs a heart valve transplanted. Heart valves don't have to be transplanted from another person. They can be replaced by a metal valve, or the surgeon can create a new valve from a different part of the patient's body. There was no reason to wait for a donor valve when they had other options available.

Continuity: Season 5 - Episode 9: My Half-Acre: When JD and Julie have had their old couple photograph, JD takes his mask off and his hair is flat. In the next shot, it is waxed up and styled again.