Health care workers have a high prevalence of sickness absence because of low back pain (LBP). This study examined whether fear-avoidance beliefs (FAB): 1) predicted sickness absence and 2) moderated the association between LBP and sickness absence among 1724 newly educated health care workers with LBP ≥ day during the previous 12 months. High FAB was associated with sickness absence days 1 year later (relative risk, 1.45, 95% confidence interval = 1.24 to 1.70), controlled for LBP, previous sickness absence, and age. When controlling for work environmental factors, the association remained significant but decreased. Furthermore, the results showed that health care workers with high degree of LBP would have more sickness absence days if they also had high FAB. To reduce sickness absence, education about pain management must be presumed to be beneficial.