The present dissertation consists of three empirical studies on social anxiety disorder (SAD) in a sample of Swedish children and adolescents. Based on findings made in a large behavior treatment study, the thesis contributes to the field of research on childhood SAD by investigating a factor that maintains the disorder, ways to measure and screen for diagnosis, and the treatment of the disorder. Study I investigated whether giving an educational course to the parents of socially anxious children would lead to a better outcome of a behavior-treatment study consisting of individual and group treatment components such as exposure in-vivo and social skills training, compared to a condition where only children were treated and the parents received no educational course.  Another purpose of Study I was to investigate what influence, if any, co-morbidity has on treatment outcome. The results showed that there was no significant difference between the two treatment groups on any of the primary or secondary outcome measures. Further, the comorbid disorders did not impair the SAD treatment but was rather associated with further improvement, and despite the sole focus on SAD, there was significant improvement in the comorbid disorders. Study II tested the psychometric properties of the Social Phobia and Anxiety Inventory for Children in a sample of children with SAD. The results indicated that the instrument is a both valid and reliable measure. Further, a three-factor solution represented the three areas of SAD commonly found in adult studies, i.e. fear of performance, observation, and interaction situations. Study III explored threat perception and interpretation bias by means of an ambiguous stories task. The results showed that children with SAD deviated significantly from a non-anxious control peer group with regard to their interpretations. Post treatment the threat perception bias was altered in a normal direction, and one year after treatment termination, the SAD sample ratings were comparable to those of the non-anxious children.