This trial examined stepped-care cognitive-behavioral treatment (CBT) among 96 autistic youth with co-occurring anxiety. Step 1 included an open trial of parent-led, therapist-guided bibliotherapy. Step 2 was family-based CBT for those who did not respond to Step 1 or maintenance for those who did. Eighteen participants (28%) who completed Step 1 responded. Responders reported significantly lower pre-treatment anxiety, internalizing symptoms, and functional impairment than non-responders. After Steps 1 and 2, 80% of completers (55% intent-to-treat) were responders. Anxiety, impairment, and ASD-related impairments significantly improved. Youth in maintenance experienced faster improvement through post-treatment, though there were no group differences at 3-month-follow-up. A stepped approach may help some individuals in Step 1, particularly those who are less anxious.