One in six patients is being wrongly diagnosed by doctors - which means they are being given drugs or treatments that are useless while their real problem is being overlooked.
And researchers admit that wrong diagnosis could be even more prevalent than their figures suggest. Their estimates are based on cases that are reported, and many more may be going unrecorded, either because the patient or doctor does not immediately realise the misdiagnosis has happened, or because the doctor wants to cover up the mistake.
The figures are based on doctors working within the UK's National Health Service (NHS), although misdiagnosis is a universal problem. A study published in the American Journal of Medicine reported that 15 pr cent - or one in six - cases in developed countries was misdiagnosed.
Researchers from Imperial College London say the problem is more common among junior doctors, who are sometimes too quick to arrive at a diagnosis or are reluctant to consult a more senior colleague.
(Source: Daily Telegraph, September 22, 2009).