Understanding prognosis is important in managing low back pain. In this article, we discuss the available evidence on low back pain prognosis and describe how prognostic evidence can be used to inform clinical decision making. We describe three main types of related prognosis questions: 'What is the most likely course?' (Course studies); 'What factors are associated with, or determine, outcome?' (Prognostic factor or explanatory studies); and 'Can we identify risk groups who are likely to have different outcomes?' (Risk group or outcome prediction studies). Most low back pain episodes are mild and rarely disabling, with only a small proportion of individuals seeking care. Among those presenting for care, there is variability in outcome according to patient characteristics. Most new episodes recover within a few weeks. However, recurrences are common and individuals with chronic, long-standing low back pain tend to show a more persistent course. Studies of mixed primary care populations indicate 60-80% of health-care consulters will continue to have pain after a year. Important low back pain prognostic factors are related to the back pain episode, the individual and psychological characteristics, as well as the work and social environment. Although numerous studies have developed prediction models in the field, most models/tools explain less than 50% of outcome variability and few have been tested in independent samples. We discuss limitations and future directions for research in the area of low back pain prognosis. Copyright 2009 Elsevier Ltd. All rights reserved.