Patients are being put at risk because hospital doctors are not being given proper clinical handovers when they come on shift, research suggests.
The study authors said handovers were haphazard
A survey of house officers on call in general surgery in 17 hospitals in Wales found clinical handovers to be unstructured and haphazard.
The authors said doctors were often left unaware of patients' conditions or even that they had been admitted.
The study appeared in the British Medical Journal.
Ludger Barthelmes, specialist registrar at West Wales General Hospital in Carmarthen, said the research was prompted by his experience of a lack of a proper handover when he was on call.
He told the BBC News Website: "It makes things awkward.
"Sometimes investigations have to be redone, tests which have been asked for or X-rays that have been asked for have to be repeated because we are simply not made aware of it."
Agreeing that missing information could sometimes put patients at risk, he said: "If you don't follow up on certain test results or if you are not aware of certain conditions that have been discovered then you can miss the opportunity to do something about it."
Another problem his research uncovered was that sometimes on call staff were simply not made aware that patients had been admitted at all.
In their survey of house officers, the team found that only in two hospitals had a set method of handover been developed which gave information on outstanding investigations and tests and patient reviews.
In most hospitals, patient lists were used instead that had the potential for patients to be "lost" if the lists were mislaid, the team said. Six hospitals had no allocated place for handovers.
"It became clear that the handover is not structured in anyway - it's haphazard and done without supervision."
The doctors called for a formal clinical handover process to be set up.
They said things had got worse after the European Working Time Directive limited doctors' shifts to 13 hours.
This meant that many UK hospitals had moved to full or partial shift systems which did not necessarily marry with the on-call and day rotas of more senior staff.
The researchers suggested rotas should be adjusted to allow sufficient overlap between junior doctors and more senior doctors' working days.
Dr Andrew Rowland, of the British Medical Association's junior doctors committee, said patient safety was compromised unless proper handover procedures were followed.
He said work that he and others at the BMA carried out had led to guidelines being drawn up on what to hand over, how and by whom.
They were widely welcomed by doctors and health trusts alike.
He added: "I am really pleased these doctors have come forward to highlight these problems.
"But if handovers are not being organised properly it is really a failing of the organisations for whom they are working."
Sue Dean is NHS National Workforce Projects, the organisation charged with helping the NHS in England to adopt new methods to meet the target of the European working time directive.
She said: "Handover is an important element of the new junior doctor shift system.
"The evidence shows that handover is happening and that some hospitals have already adopted effective new systems of best practice to support the process.
"However, these best ways of working need to be universal and work we are currently undertaking involves pilot sites that will look at different ways of ensuring that handover works well for the benefit of staff and patients."