The study included more than 420,000 Danes who got their first cell phone between 1982 and 1995.
Some of those people kept their phones as long as 21 years. But, on average, they had cell phone service for 8.5 years.
The study's researchers included Joachim Schuz, PhD, of the Danish Cancer Society. It tracked cancers among the cell phone users from the start in 1982-1995 through 2002.
During that time, the group had 14,249 cancers.
But that's slightly less than Denmark's expected cancer rate for the general population, the researchers note.
The data show no increase in brain cancer, leukemia, or tumors of the eyes or salivary glands among cell phone users.
These findings extend Schuz's 2001 study, which showed no rise in cancer risk among the same cell phone users over a shorter period of time (three years).
"We found no evidence for an association between tumor risk and cellular telephone use among either short-term or long-term users," the researchers write.
Concerns about cancer had been raised because "during operation, the antenna of a cellular telephone emits radio frequency electromagnetic fields that can penetrate 4-6 cm into the human brain," they note.
But most studies have found no association between cell phone use and brain cancer, write Schuz and colleagues.
Why were cancer rates a bit lower than expected among the cell phone users?
That's not clear from the study, but perhaps cell phone users have healthier lifestyles, the researchers say.
They say their findings are "reassuring" and call for further follow-up, since cell phones are relatively new and cancer can take a long time to develop.
SOURCES: Schuz, J. Journal of the National Cancer Institute, Dec. 6, 2006; vol 98: pp 1707-1713. News release, Journal of the National Cancer Institute.
By Miranda Hitti
Reviewed by Louise Chang