Danish researchers who conducted the world's biggest study into mobile phone use say they have found no evidence suggesting an increased risk of brain cancer.
In a study reported in the British Medical Journal, the researchers monitored the health of more than 350,000 phone users aged over 18.
They say long-term phone users showed no higher likelihood of developing cancer, but refused to rule out the possibility of a small and moderate increased risk for very-heavy users.
Previous research into the possible carcinogenic effects of mobiles has long been considered inconclusive, party due to the lack of long-term data.
Some of the users were worried that the electromagnetic fields emitted by their mobiles could contribute to brain or neck tumours.
But researchers with Copenhagen's Institute of Cancer Epidemiology found that long-term use is not associated with a higher risk.
An Australian expert in the field, Rodney Croft, professor of health psychology with the University of Wollongong, said he is not surprised by the findings.
"To be honest I think it's what we would have expected. I think that it does provide a strong indication that there isn't a relationship between mobile phone use and cancer," he said.
Dr Croft says the study should go some way to alleviating widespread perceptions of a link.
"There has been a lot of talk about with the increase in mobile phone usage that there has also been an increase in brain tumours. And I think that this suggests that those kind of statements aren't very accurate," he said.
"In Australia we have some neurosurgeons for instance who say that they see a lot more people come into their clinics with brain tumours and attribute these to mobile phone use.
"But what this really says is that there isn't such an increase. It's more likely to be that they happen to have a large number go through their particular clinic or maybe people have heard that they are sympathetic to the idea that mobile phones may cause the brain tumour and so end up there - very difficult to know.
"But certainly when we look at large numbers we just don't see this kind of increase."
No guarantee
But he has warned the study is not a guarantee of no link.
"The main issue however is that it's not the kind of design that we could be 100 per cent confident with," he said.
"There are a number of limitations, for instance the way that they determine whether someone has used a mobile phone is based on whether they had a subscription to a mobile phone. But of course someone could have a subscription and not actually use it, their spouse or child for instance might use it.
"So it's not 100 per cent certain that the exposures are actually accurate."
But he says it reaffirms the basic science that indicates mobile phone usage does not have any effect on the brain.
"The only mechanism that we know by which a mobile phone can interact with the body is through heat. And the amount of heat that comes off a mobile phone is extremely small... about 0.1 of a degree, and that's very, very small compared to the normal fluctuations in temperature of the brain.
"So certainly going back to basics we don't know of any reason why there would be an increase in cancer."
Professor Croft says extensive animal testing has also confirmed this.
"There has been a lot of animal work looking to see whether any of the processes that are related to cancer may be affected by mobile phones. And we don't see it with animals either," he said.
"Supposing we didn't have a reason but we saw a big increase [in brain tumours] then we'd have to think seriously about whether our basic science, the animal science for instance, was good enough.
"But until we actually see an increase I personally don't think that there is any real reason to be concerned."
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