The burden of low back pain disability has increased steadily over the last few decades in western countries. The high social and economic cost of low back pain is related to the minority of individuals who lose more than six months from work. Although the risk factors for low back pain have been well delineated, methodologic obstacles have hindered the collection of information on factors associated with a chronic course. The most reliable data are those generated by prospective studies involving multivariate analyses. Advanced age is associated with an increased risk of chronic pain, as is male gender (except in some recent studies). Weight and height are not related to chronicity. Disease-related factors predictive of chronic pain include presence of multiple functional symptoms, evidence of nonorganic disease, pain in the legs, significant disability at onset, a protracted initial episode, multiple recurrences and a history of low back pain or inhospital treatment. Occupational factors have a very substantial impact: workers in blue-collar jobs, those involved in heavy labor or in jobs that require efforts beyond their physical capabilities and those who have a low level of job satisfaction or poor working conditions, who are new at their job, or who are not well rated by their superiors are more likely to develop chronic pain. A history of compensation for a spinal condition, receipt of work-related sickness payments, or litigation about compensation are also associated with an increased risk of chronic pain. Social and economic factors predictive of a chronic course are a low level of schooling, language problems, a low income and an unfavorable family status. The impact of psychological factors is controversial. Depression, a number of specific coping strategies and a sensation of being "sick all the time" may be associated with an increase in the risk of chronicity. Overall, progression to a chronic pattern of pain is more closely dependent on demographic, psychosocial and occupational factors than on the medical characteristics of the spinal condition itself. Simple questionnaires can be used to identify patients at a high risk for chronicity. Treatment should be prompt and comprehensive in these patients since the likelihood of a return to work decreases rapidly as sick leave duration increases.