Key words: occupational injuries, back problems, secondary diagnoses I believe Zwerling and Ryan [1991] may have overlooked a significant confounder to their data on non-back occupational injuries in laminectomy patients. In that study, the authors reported that low back injured employees had no significant increase in duration of disability from non-back injuries. They concluded that physiologic rather than psycholsocial factors provide the more likely explanation for prolonged disability in back injuries. Their screening looked for separate, non-back injuries in these patients, but I saw no evidence that they looked for such reports of problems as secondary diagnoses where the primary diagnosis was recurrent low back pain. My own experience is that an event resulting in injury to multiple body parts will be recorded in the category considered to be pre-existing or most important. Therefore, for example, an individual with known back problems who sustains a fall injuring the back and knee will be evaluated and recorded primarily for the diagnosis of back injury. Alternatively, knee problems might be blamed on "changes in gait" attributed to the back problem. Therefore, I would wonder whether Zwerling and Ryan's results might not be significantly changed if secondary diagnoses of a nonback nature were diligently searched for in the actual medical records relating to the subsequent injuries recorded as "back.