The present dissertation consists of three empirical studies on children and adolescents presenting with various specific phobias in Stockholm, Sweden and in Virginia, USA. The overall aim was to contribute to our understanding of childhood fears, anxiety and phobias and to evaluate the efficacy and portability of a one-session treatment of specific phobias in youth. Study I tested the dimensionality of the Parental Bonding Instrument, across three generations and for two countries, and examined if parenting behaviors of indifference and overprotection were associated with more anxiety problems in children. The results showed that the four-factor representation of parental behavior provided an adequate fit for the instrument across informants. Perceived overprotection was associated with significantly more anxiety symptoms and comorbid diagnosis in children. Study II explored parent-child agreement on a diagnostic screening instrument for youths. The results indicated that children scoring high on motivation at treatment entry had generally stronger parent-child agreement on co-occurring diagnoses and severity ratings. Parents reported overall more diagnoses for their children, and parents who themselves qualified for a diagnosis seemed more tuned in to their children’s problematic behavior. Study III compared a one-session treatment with an education-supportive treatment condition, and a wait-list control condition for children presenting with various types of specific phobias. The results showed that both treatment conditions were superior to the wait-list control condition and that one-session exposure treatment was superior to education-supportive treatment on several measures. Treatment effects were maintained at a 6-month follow-up. Overall, the above findings suggest that the one-session treatment is portable and effective in treating a variety of specific phobias in children and adolescents.