The authors' case-control study on the possible association between brain tumors and mobile and cordless telephone use included 1,617 patients and 1,617 controls. A questionnaire was answered by 1,429 (88%) cases and 1,470 (91%) controls. Use of analog cellular telephones yielded an odds ratio (OR) for brain tumors of 1.31, 95% confidence interval (CI) = 1.04-1.64, increasing for ipsilateral use to OR = 1.65, 95% CI = 1.19-2.30. The authors found the highest risk for the 20-29-yr age group, with OR = 5.91, 95% CI = 0.63-55 for ipsilateral use of analog phones. The highest risks were associated with >5-year latency period in the 20-29-yr age group for analog phones (OR = 8.17, 95% CI = 0.94-71), and cordless phones (OR = 4.30, 95% CI = 1.22-15).