What factors affect how long it will take to return to work following acute low-back pain? A systematic review update by the Institute for Work & Health (the original was published in 2005) aimed to find what new information was emerging from the research literature. The goal was to assess the evidence on factors that are present at the beginning of a work absence due to low-back pain that may predict the duration of sick leave. The findings of this systematic review update are included in this report.