We describe the Smart Ageing, a serious game in a 3D virtual environment aimed at the early detection of Mild Cognitive Impairments in persons ageing between 50 and 60, and at assessing cognitive impairments in persons already diagnosed or having neurodegenerative dementia. Smart Ageing is a telematic system in which users realize a set of screening tests structured in five daily-life tasks in a familiar environment addressing various cognitive skills: memory, executive functions, divided attention, short-term and long-term memory and spatial orientation and attention. The game integrates novel accessibility features to make it usable by seniors. Several indexes of evaluation are registered while users perform the test, that provide a complete picture of the user's behavior during the game. The design and implementation of the game has been realized following a usercentered agile methodology that has allowed to reine the tasks and enhance the technology throughout the development stage. The game is currently in a validation stage on a sample of 1000 users. The results of the electronic test are been compared to standard pen-based tests. We except that the validation will confirm Smart Ageing as a powerful screening tool for the early detection of cognitive impairments on a wide scale, otherwise impossible using the traditional pen-based test.