Expectancies for a favorable treatment outcome have been associated with actual favorable outcomes but have been understudied in youth with anxiety. The current study applied structural equation modeling in a sample of anxious youth (N = 488; 7–17 years, M = 10.69, SD = 2.80) to examine whether a multi-informant latent expectancies factor, indicated by youth, parent, and therapist reports, predicted a latent posttreatment anxiety factor, controlling for a latent pretreatment anxiety factor. Both anxiety latent factors were indicated by youth, parent, and independent evaluator (IE) reports. Analyses also examined whether treatment condition (cognitive behavioral therapy, sertraline, combination, pill placebo) moderated the association between expectancies and outcome, and whether this association differed across development. Findings indicated that informant reports loaded similarly onto the latent factors. Results also demonstrated that treatment expectancies were positively associated with outcomes, and that this relationship held across treatment type and age group. Treatment implications and future research directions are discussed.