BACKGROUND AND AIMS: According to the concepts of 'use it or lose it' and cognitive reserve, cognitively challenging activities may boost cognitive abilities in older adults. Using computers and the internet provides divergent cognitive challenges to older persons, and the positive effects of computers and internet use on the quality of life have been found in earlier studies. METHODS: We investigated whether prolonged guided computer use by healthy older adults (64-75) may be beneficial to cognitive ability in a randomized controlled study. The intervention consisted of brief training and subsequent use of a personal computer with an internet connection at home for a 12-month period. 191 participants were randomly assigned to three groups: Intervention, Training/No intervention, or No training/No intervention. A fourth group consisted of 45 participants with no interest in computer use. The effect of the intervention was assessed by a range of well-established cognitive instruments that probed verbal memory, information processing speed, and cognitive flexibility. Data were collected at baseline and after four and twelve months. RESULTS: Intensive interaction with a personal computer with standard software applications had no effect on cognitive measures; no differences in changes in cognitive parameters over time were found between groups. CONCLUSION: Learning to use a computer and the internet does not benefit healthy, communitydwelling older adults with respect to many domains of cognitive functions. The implications of these findings for future studies that use cognitive challenge to counteract usual cognitive aging are discussed.