Many people with early dementia can drive safely, a survey has suggested.
Cognitive tests cannot determine safe or unsafe drivers
The risk of crashes among Alzheimer's patients is "acceptably low" for up to three years after the disease becomes clinically apparent, they claim.
The conclusions in the British Medical Journal are based on medical data published between 1966 and 2007.
Anyone holding a UK driving licence must, by law, inform the DVLA if they have a medical condition that might affect the safety of their driving.
The DVLA says that people with poor short-term memory are a higher risk and should not be driving.
Lead researcher Professor Desmond O'Neill, of the Trinity Centre for Health Sciences and Meath Hospital in the Republic of Ireland, says there is a misconception about the impact of age-related disease on driving.
He said many medical journals had reported an apparent increase in crashes per mile driven for older people, yet several studies have established that this is related to low mileage rather than to age.
And surveys of drivers aged more than 80 consistently show prudent driving behaviours, said Professor O'Neill.
He says the challenge for doctors and the licensing agency is to balance mobility and safety in a growing population of older drivers.
Stopping driving can limit access to family, friends, and services and is an independent risk factor for entry into a nursing home, he said.
Professor O'Neill said: "Mobility is a key component of healthy and successful ageing.
"People with early dementia tend to be very safe drivers and they tend to limit their own driving themselves when they deteriorate."
He said driving was a complex skill and that it was impossible to assess competency and safety with "dementia" cognitive tests.
Age is no bar to the holding of a driving licence
Licences are normally valid until age 70
At age 70, the agency requires confirmation that no medical disability is present
After 70, the maximum licence period is three years, subject to a satisfactory completion of medical questions
Drivers have an obligation to declare medical conditions that may affect driving safety
The patient's doctor will also be asked for their professional opinion
A formal driving assessment may be necessary
A driving licence may be issued subject to annual review
He said there was a need for more centres offering formal driving assessments.
Clive Evers, of the Alzheimer's Society, said: "Many people with dementia are able to continue driving safely after being diagnosed and the time when they must give it up is different for each individual.
"It is essential that people with dementia undergo regular reviews to ensure their safety is balanced with their mobility. A good assessment will incorporate the views of friends and family who are familiar with the individual's driving behaviour.
"Tests to assess driving competence are currently limited and more research is needed on the subject.
The UK Department for Transport is due to launch a public consultation to consider changes to relicensing.
But a DVLA spokesman said: "There are currently no plans to amend the licensing arrangements for drivers with dementia."