Improved information on the natural history of back pain is needed to enable doctors and their patients to understand the likely course of back pain and to evaluate whether alternative interventions are preferred over self care or watchful waiting. The course of back pain is highly variable, occurring in transient, recurrent, and chronic phases. Recent longitudinal studies suggest that back pain is typically a recurrent condition and that chronic phases of back pain occur more often than previously believed. New methods of studying the course of back pain, standardized definitions of phases in the natural history of back pain, and improved outcomes data are needed to better understand the short-term and long-term course of back pain.