According to the experts, the chances of developing a malignant tumor are "significantly increased" for people who use a mobile for ten years.
The shocking finding is the result of the biggest ever study by the International Agency for Research on Cancer, part of the World Health Organisation.
The experts found a type of brain tumor called glioma is more likely in long-term mobile users.
French experts analyzed data from 13 countries, including Britain.
Although researchers admit the cause is unknown, but according to them radiation from handsets could be the trigger.
"To underestimate the risk would be a complete disaster," the Sun quoted study chief Professor Elisabeth Cardis, as saying.
However, a British expert insisted mobiles are not dangerous.
Professor Patricia McKinney of the University of Leeds said: "Reasonable use is unlikely to increase the risk of tumors."