Objective: Conduct a systematic review of low back pain cost of illness studies. Methods: Medline was searched to uncover studies about the direct or indirect costs of low back pain published in English from 1997 to 2007. Data extracted for each eligible study included study design, population, definition of low back pain, methodology for estimating costs, year of data, and estimates of direct, indirect, or total costs. Results: The search yielded 147 studies; 27 were deemed relevant. The studies reported on data from Australia, Belgium, Japan, Korea, the Netherlands, Sweden, the UK, and the US. Nine studies estimated direct costs only, 9 indirect costs only, and 9 both direct and indirect costs, from a societal (n=18) or private insurer (n=9) perspective. Methodology used to derive both direct and indirect cost estimates differed markedly among the studies. Among studies providing a breakdown on direct costs, the largest proportion of direct medical costs for low back pain was spent on physical therapy (17%) and inpatient services (17%), followed by pharmacy (13%) and primary care (13%). Among studies providing estimates of total costs, indirect costs due to lost work productivity represented a majority of overall costs associated with low back pain. Three studies reported that estimates with the friction period approach were 56% lower than with the human capital approach. Conclusion: Estimates of the economic costs in different countries vary greatly depending on study methodology but by any standards must be considered a substantial burden on society. This review did not identify any studies estimating the total costs of low back pain in the US from a societal perspective. Such studies may be helpful in determining appropriate allocation of health care resources devoted to this condition.