This article describes the development of a classification system to measure the expertise levels of practicing paediatric rehabilitation therapists. Seventy-five therapists from five disciplines (physical, occupational, speech-language, behaviour, and recreational therapy) were involved, along with 170 peers, and 188 parents of children with disabilities. A cluster analysis of 10 indicators of expertise (derived from a battery of self-completed, peer-completed, and parent-completed measures) indicated three levels of therapist expertise--novice, intermediate, and expert. Expertise level was related to various aspects of experience but not to therapy discipline. The classification system will be useful for the education and professional development of paediatric therapists, and for research on expertise in paediatric rehabilitation. (Contains 4 tables.)