Stroke is a major cause of death and disability. In order to prevent stroke, knowledge of risk factors is essential. This thesis aims to build on the expanding knowledge of stroke risk factors, by using data from the Oslo Ischemia Study. The candidate studied the impact of potential novel risk factors obtained from an exercise test. Further, he investigated the impact of change in fitness and body weight during adult life. Prestgaard found that blood pressure and heart rate measured during exercise added prognostic information, even when taking into account traditional risk factors. He also observed that becoming fit during middle-age halved the risk of stroke, compared to remaining unfit. The opposite was true for those becoming unfit, which saw their stroke risk double. Lastly, he examined weight changes during two different time periods of adult life and found that weight gain during early adult life was associated with increased stroke risk. This was not found for those gaining weight during mid-life. These findings can help physicians identify those at heightened risk of stroke, while also serve as a basis for public health management strategies.