Patients were accidentally sent a text from their GP on Christmas Eve telling them they had terminal lung cancer.
Askern Medical Practice, near Doncaster, South Yorkshire, then sent another message an hour later wishing everyone a "Merry Christmas".
Hundreds of people registered at the surgery are understood to have received the diagnosis in error.
With confused patients desperately trying to get answers, the practice then sent an apology.
The initial text asked for “a DS1500 for the above patient. Diagnosis — Aggressive lung cancer with metastases”.
DS1500 is the form that people with terminal illnesses use to claim benefits and “metastases” means a cancer has spread and is almost certainly incurable.
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Vicky Southgate shared the message on Facebook and said she was "shaking and close to tears".
She said: "Something's clearly not right at Askern Medical Practice. Fuming. I received this message and I’m not the only one. I was shaking and close to tears.
"Quite a few in the surgery now with the same text .
"I was near the surgery and walked in to say what the hell? I’m not the only one but people will now be worried if they’ve received this text."
Kerry Marie said: "I got same message, I was raging. After total shock and worry my heart sank . Absolutely disgraceful."
Others questioned why such information, if it was legitimate, would be sent so informally as a text to begin with.
Chris Reed said his partner burst into tears.
The 57-year-old said he tried to ring the surgery but the lines were busy so he raced down there before being eventually told his results were negative.
He told the Sun : “They went from, ‘You’ve got lung cancer’ to ‘Merry Christmas’ in about an hour. Unbelievable.”
A second text from the surgery said: "Please accept our sincere apologies for the previous text message sent.
"This has been sent in error.
"Our message should have read we wish you a merry Christmas and Happy New Year."
The Mirror has contacted Doncaster CCG for comment.
