Physical activity has drawn a lot of attention in terms of being able to increase life satisfaction. The aim of this thesis was to investigate and understand the relationship between life satisfaction and physical activity. We were also interested in the relationship between best friend´s physical activity, the individual's own physical activity and life satisfaction. The study used data from the Norwegian Longitudinal Health Behaviour Study, following 474 23 year olds until age 30 in 2007. Correlation analysis and regression analysis were conducted. The results showed surprisingly no significant positive correlation between life satisfaction and physical activity. Best friend´s physical activity was low, but significantly correlated with physical activity 23 (r = .35) and 30 (r = .16), and also life satisfaction 23 (r = .16) and 30 (r = .23). Both physical activity and life satisfaction show moderate stability from 23 to 30 (r = .41, r = .50). The study concluded that due to methodical reasons, we did not get a significant correlation between life satisfaction and physical activity. Best friend´s physical activity is seen to be associated with a person´s physical activity, which further supports existing research. The fact that best friend´s physical activity was associated with an individual´s life satisfaction, is an interesting finding, which perhaps can highlight the importance of a physical active environment for the increase of well being and life satisfaction. Keywords: physical activity, exercise, life satisfaction, well-being, friends, positive psychology