It's enough to make anyone crazy. The radiation from cell phones is invisible, impossible to measure without instruments -- and yet it's there, getting into your brain for several hundred minutes a month, whenever you put the phone to your ear. Most people can't help wondering just a little if they've been doing themselves harm. But has the explosion of cell phones onto the world scene caused an increase in brain tumors? A study in the Journal of the National Cancer Institute -- a big one -- says no. The authors, led by Isabelle Deltour of the Institute of Cancer Epidemiology at the Danish Cancer Society, pored through public health statistics from Denmark, Finland, Norway, and Sweden, where medical record-keeping has historically been very detailed. They crunched the numbers from 1974 to 2003, during the period when cell phones grew from zero to near-ubiquity. 16 million adults were included in the records. The authors looked for two types of brain tumors, glioma and meningioma. 59,984 people were diagnosed with them during the study period. The key line: "No change in incidence trends were observed from 1998 to 2003, the time when possible associations between mobile phone use and cancer risk would be informative about an induction period of 5–10 years." The abstract of the study is HERE, and the complete paper is HERE. Some numbers from it: "From 1974 to 2003, the incidence rate of glioma increased by 0.5% per year (95% confidence interval [CI] = 0.2% to 0.8%) among men and by 0.2% per year (95% CI = –0.1% to 0.5%) among women and that of meningioma increased by 0.8% per year (95% CI = 0.4% to 1.3%) among men, and after the early 1990s, by 3.8% per year (95% CI = 3.2% to 4.4%) among women." That said, the researchers caution that this is probably not the final word. It is hard, of course, to prove a negative. The authors say it may be that tumors from cell phones take more time to develop; that there may be people who are more vulnerable than others, but their numbers were hidden in the mass of data; or that the increased risk really is very small. That said, the study does seem to calm the fears about cell phones and cancer. Cell phones and driving are another matter.