Although information exists on the cost of workers' compensation low back pain (LBP), there is limited information on the duration of lost work time as well as the association between cost and duration. For this study, cost and duration of lost work time information were derived from a large workers'compensation company's database for 1992 LBP claims (n = 106,961). The distribution of cost was skewed, with an average cost of a claim being 20 times higher than its median. A disproportionately small percentage of the costliest LBP claims (10%) were responsible for a large percentage of the total cost (86%). The distribution of length of disability (LOD) was also skewed, with an average of 102 days and a median of zero. The average and median LOD for those claims with at least one day of compensable disability was 303 and 39 days, respectively. As a "rule of thumb," it was found that of those claimants who remain on disability at the end of n weeks, approximately 50% will be off disability at the end of 6·n weeks. Additionally, the 7% of the claims with an LOD greater than one year accounted for 75.1% of the cost and 84.2% of the total disability days. Disability days that were accrued after one year of disability accounted for 59.3% of the total number of disability days. This result suggests that other LOD estimation techniques, which may not account for disability days beyond one calendar year (eg, the Bureau of Labor Statistics Annual Survey of Occupational Injuries and Illnesses), may result in a marked underestimation of LOD.