The Pediatric Evaluation of Disability Inventory (PEDI) is a useful clinical and research assessment, but it has limitations in content, age range, and efficiency. The purpose of this article is to describe the development of the item bank for a new computer adaptive testing version of the PEDI (PEDI-CAT). An expanded item set and response options were reviewed by clinician experts and examined at parent and clinician focus groups. Eleven parents participated in 32 cognitive interviews to examine content, format, and comprehension of items and responses. A set of 76 self-care, 78 mobility, and 64 social function items with pictures and a four-point "Difficulty" scale were developed. The PEDI's Caregiver Assistance scale was replaced by a "Responsibility Scale" with 53 items. Content validity was established incorporating input from clinicians and parents. The new item bank covers a broad range of functional activities for children of all ages and abilities.