Low-back disorders (LBD) continue to be the most costly and common musculoskeletal problem facing society today. Investigators have developed tools or measures that are intended to identify jobs that will probably be associated with an elevated risk of low-back disorders. However, an important and not widely discussed issue associated with these tools and procedures has been that of the validity or effectiveness of the tools. Therefore the objective of this study was to evaluate the validity and effectiveness of two commonly used types of LBD assessment methods in terms of their ability to correctly associate jobs with LBD risk. The 1981 NIOSH Work Practices Guide for Manual Lifting and the 1991 NIOSH revised lifting equation, along with psychophysical measures were assessed for their ability to correctly identify high-, medium-, and low-risk (of LBD) jobs. Risk was defined according to a database of 353 industrial jobs representing over 21 million person-hours of exposure. The results indicated that both NIOSH measures were predictive and resulted in odds ratios between 3.1 and 4.6. Higher odds ratios were found when the maximum horizontal distance was used to assess a job compared to the average horizontal distance. Further analyses indicated that the two NIOSH assessment methods classified risk in very different ways. The 1981 NIOSH Guide demonstrated good specificity (91%) in that it identified low-risk jobs well but it also displayed low sensitivity by only correctly identifying 10% of the high-risk jobs. The 1993 NIOSH revised lifting equation, on the other hand, had better sensitivity. It correctly identified 73% of the high-risk jobs but did not identify low- and medium-risk jobs well. Using psychophysical criteria it was observed that 60% of the high-risk jobs would be judged to be acceptable, whereas, 64% and 91% of the medium- and low-risk jobs, respectively, would be judged to be acceptable. This study indicates that the different measures have various strengths and weaknesses. When controlling for occupational LBD it should be recognized that a variety of measures exist and that the measure that most appropriately assesses risk depends upon the characteristics of the job.