Human beings are social creatures. Accordingly, fear of social situations can be severely disabling. Social anxiety disorder (SAD) is characterized by excessive fear of negative evaluation in social or performance situations. SAD has an early onset and often goes undetected an untreated. Descriptive studies on non‐clinical samples are required in order to find ways to prevent SAD and associated consequences. This thesis aimed at examining epidemiological variables of SAD in adolescence which is the critical period for onset of SAD. More exactly, issues of detection and prevalence, victimization and developmental course were addressed. Data was collected in four different community samples, using cross‐sectional and longitudinal designs. In the first study (n=169), psychometric evaluation of a screening questionnaire for use with adolescents was conducted. The second study (n=2128) investigated prevalence of SAD in students in grade 6‐8 (age 12‐14 years). In the third study (n=3211), the association between SAD and victimization in high‐school students (aged 17) was investigated. Finally, in the fourth study (n=350), longitudinal associations between social anxiety and depressive symptoms were investigated, with 4 waves of data from grade 7 to grade 11. Self‐reported SAD was found among 4.4% of students in grade 6‐8 and among 10.6% of high‐school students. Females reported SAD to a significantly higher degree than males in all age groups. Experiences of peer victimization, maltreatment and sexual victimization were significantly more common in those reporting SAD than in non‐cases. Social anxiety was stable over adolescence. Further, peer victimization in grade 7 predicted social anxiety that mediated subsequent depressive symptoms. In conclusion, self‐reported SAD is common in Swedish adolescents and especially in girls and older adolescents. Social anxiety is stable over adolescence and correlated with depressive symptoms over course. The high prevalence rates, stable course and mediation of depressive symptoms call for early detection and prevention of social anxiety. The relationship between victimization and SAD needs to be investigated further in controlled prospective studies on children and adolescents.