According to recent nationwide surveys there have been dramatic increases in stress and serious stress-related health problems among Swedish adolescents. The aims of the present thesis were to investigate the prevalence of perceived chronic stress among sixteen-year-old adolescents who attended their first year at high-ranking high schools in the Stockholm area, to examine if factors that have been found to be relevant in the development of chronic stress among adults also contribute to chronic stress among adolescents, and to investigate the associations between chronic stress and sleep-related variables and academic achievement. Data were collected by means of self-report instruments. The main outcomes showed that a substantial number of individuals (30%) reported to perceive severe stress symptoms. The highest degree was perceived by 8% who suffered from symptoms to an extent which otherwise only has been observed among adult clinical burnout patients. Besides, 15% reported severe stress symptoms throughout high school and were thus considered to suffer from chronic stress. Perceived high demands, low global self-esteem, sleep disturbances and low social support were crucial factors in explaining stress symptoms. Another finding showed that perceived chronic stress was associated with adolescents’ academic achievement. A closer look at the potential contribution of sleep-related variables to academic achievement revealed further that, apart from severe stress symptoms, social jetlag was involved in predicting variation in academic achievement. Overall, the findings indicated that there is a high prevalence of chronic stress among adolescents. The results should be taken seriously, as young people’s sense of well-being during this period impacts both their successful transition into adulthood and their life course. Future research options and potential practical applications in terms of chronic stress prevention were suggested and discussed.