Symptoms of mental disorders commonly begin in the early adolescent years. However, whether they are indicative of the risk of young people developing serious mental disorders remains unclear. Such symptoms assessed in young people in clinical or high-risk settings have provided support for ‘staging’ models for serious mental disorders. In these models, sub-threshold symptoms are hypothesized to progress to later stages of psychosis and mood disorders. In order to understand whether such staging models are valid for young people in the community, it is necessary to study cohorts of young people recruited from the community who are prospectively followed over time. Such cohorts also help avoid biases associated with selecting participants or their recall of symptoms. We propose to examine the ALSPAC cohort to determine whether subthreshold mood and psychotic symptoms in early adolescence progress to later stages (threshold stages) of these disorders, or predict difficulties in functioning in young adulthood. Specifically, we will examine the symptoms of mania, depression and psychosis in young adulthood. We propose to compare those with and without progressive symptoms of these mental disorders with respect to their birth, early life and parental characteristics in order to identify predictors of later difficulties. We also propose to examine the role of intermediate or late adolescent life events or substance use in the progression of mental health symptoms. This project could help young teenagers and their families understand the risk factors that predict better or worse outcomes in the following decade. This could help plan further interventions for at least a sub-proportion of these youth.