Fortunately, the doctor realised the loss, and the printed documents were recovered by London Transport at the train's termination point and returned to the doctor.
North West London Hospitals NHS Trust reported the data breach to the Information Commissioner's Office (ICO) in May 2010.
The trust's CEO, Fiona Wise, has signed a formal undertaking to ensure that personal data is processed in accordance with the Data Protection Act.
The trust has agreed to use pseudonyms so that patients' names will not be contained in print outs.
This story was first published by Computer Weekly