The development of valid classification methods to assist the physical therapy management of patients with low back pain has been recognized as a research priority. There is also growing evidence that the use of a classification approach to physical therapy results in better clinical outcomes than the use of alternative management approaches. In 1995 Delitto and colleagues proposed a classification system intended to inform and direct the physical therapy management of patients with low back pain. The system described 4 classifications of patients with low back pain (manipulation, stabilization, specific exercise, and traction). Each classification could be identified by a unique set of examination criteria, and was associated with an intervention strategy believed to result in the best outcomes for the patient. The system was based on expert opinion and research evidence available at the time. A substantial amount of research has emerged in the years since the introduction of this classification system, including the development of clinical prediction rules, providing new evidence for the examination criteria used to place a patient into a classification and for the optimal intervention strategies for each classification. New evidence should continually be incorporated into existing classification systems. The purpose of this clinical commentary is to review this classification system, its evolution and current status, and to discuss its implications for the classification of patients with low back pain.