The Institute of Environmental Medicine at the Karolinska Institutet in Stockholm said Thursday that it has found that 10 or more years of cell phone use may increase the risk of acoustic neuroma, a noncancerous tumor, in humans. Since digital handsets have not been in widespread circulation over that period, the researchers related their findings to analog phones alone.

According to the report--based on a survey of about 150 people already diagnosed with acoustic neuroma and 600 healthy individuals--the risk of developing the tumors almost doubled for those who began using a cell phone at least 10 years beforehand. In addition, the Karolinska Institutet study contends that when the side of the head a person typically held their cell phone against was taken into consideration, the risk of acoustic neuroma was almost four times higher than normal.

The concept that wireless devices may increase the risk of brain cancer is one that has shadowed the communications industry since at least the mid-1990s, when cell phones grew more popular. However, there have been few studies that offer hard proof that a relationship exists between wireless handset use and any illness.

The U.S. Food and Drug Administration has said previously that while mobile phones do emit electromagnetic radiation, the amount of energy dispersed by the devices is similar to that emitted by other common household devices, such as television sets and microwave ovens, and does not pose a measurable health risk.

Acoustic neuroma tumors typically affect the auditory nerve, which is connected to the brain, and grow slowly over a period of years before they are diagnosed. On average, the tumors are found in less than one adult per 100,000 each year.