The Potter fans all have something called Tourette's syndrome (TS), reports the British Medical Journal.
People with TS can't help shouting loudly and violently jerking their limbs several times a minute.
Which means they hadn't been able to see COS because their tics were too noisy for the cinema.
Matthew, 14, was particularly fed up that he had missed out on seeing COS when all his mates were raving about it.
He couldn't even see it on video or DVD because it's not out until April.
But what he didn't realise was his doctor was secretly finding a magical way for him and other children with TS to see the flick.
She managed to make their dream come true and find a private cinema willing to hold a special viewing - just for them.
The jerky movements and uncontrollable noises of TS can be embarrassing and disruptive. Some young people grow out of their tics, while others are helped by medication.