Cell phones don't cause cancer, according to a major study from Denmark that tracked 420,000 Danish cell phone users -- many of them users for more than 10 years and some for more than 20 years.

In the largest ever study to yield good news about the safety of cell phones, scientists matched phone records to the Danish Cancer Registry -- a listing that records every citizen who gets the disease -- and on Tuesday, the study results were revealed.

Cell-phone users are no more likely than anyone else to develop cancer.

But the lead researcher of this massive investigation says doubts will surely linger. There is really no biological basis for concern about radio waves, he says. But people still worry.

Cell phones beam radiofrequency energy that can penetrate the outer edge of the brain, causing suspicion about the origin of various cancers. Most research has found no link between cell phones and cancer, but the phones have never been given a definite clean bill of health either.

"As the body of evidence accumulates, people can become reassured that these devices are safe," says one cell phone researcher.