OBJECTIVE: To determine whether baseline dimensions of adult insecure attachment (avoidant and anxious) moderated outcome in a secondary analysis of a randomized controlled trial comparing cognitive-behavioral therapy (CBT) plus supportive listening (CBT + SL) versus CBT plus interpersonal and emotional processing therapy (CBT + I/EP). METHOD: Eighty-three participants diagnosed with generalized anxiety disorder (GAD) were recruited from the community and assigned randomly to CBT + SL (n = 40) or to CBT + I/EP (n = 43) within a study using an additive design. PhD-level psychologists treated participants. Blind assessors evaluated participants at pretreatment, posttreatment, 6-month, 12-month, and 2-year follow-up with a composite of self-report and assessor-rated GAD symptom measures (Penn State Worry Questionnaire, Hamilton Anxiety Rating Scale, Clinician’s Severity Rating). Avoidant and anxious attachment were assessed using self-reported dismissing and angry states of mind, respectively, on the Perceptions of Adult Attachment Questionnaire. RESULTS: Consistent with our prediction, at all assessments higher levels of dismissing styles in those who received CBT + I/EP predicted greater change in GAD symptoms compared with those who received CBT + SL for whom dismissiveness was unrelated to the change. At postassessment, higher angry attachment was associated with less change in GAD symptoms for those receiving CBT + I/EP, compared with CBT + SL, for whom anger was unrelated to change in GAD symptoms. Pretreatment attachment-related anger failed to moderate outcome at other time points and therefore, these moderation effects were more short-lived than the ones for dismissing attachment. CONCLUSIONS: When compared with CBT + SL, CBT + I/EP may be better for individuals with GAD who have relatively higher dismissing styles of attachment.