While cognitive behavioral therapy (CBT) is a first-line treatment for anxiety, it is not typically offered to those with intellectual disability (ID). In this article, we provide a historical perspective on the treatment of mental health concerns in adults with ID, describe an adapted CBT treatment for anxiety in adults with Williams syndrome (WS) and mild to moderate ID, and discuss general modifications to CBT for adults with ID. Strategies used to successfully adapt CBT for adults with WS that may generalize for adults with ID more broadly include: (a) using child-based CBT manuals as a framework; (b) involving a caregiver as a therapy partner; (c) incorporating a high level of repetition; (d) simplifying language; (e) slowing the pace of instruction; and (f) incorporating specific examples and adaptations for WS.