Study Design. Systematic review. Objective. To identify the definitions of recurrence (and related recovery definitions) currently used in the literature. Summary of Background Data. Recurrence of low back pain (LBP) is a common and costly problem and the goal of many treatments is to prevent future recurrences. However, it is unclear whether standardized recurrence definitions are being used in the research literature evaluating the risk of recurrence and the effectiveness of treatments to prevent recurrence. Methods. A literature search was performed of MEDLINE, EMBASE, CINAHL, AMED, and PEDro, and from chosen systematic reviews investigating treatments that could plausibly affect recurrence of LBP. Studies were considered eligible if they investigated recurrence of LBP in a cohort of patients with LBP. Inclusion was assessed by 2 reviewers and definitions of recurrence (and related recovery) were extracted. Results. Fifty-three studies were identified by the review. Only 32% of studies gave explicit definitions of recurrence and only 10% gave a definition for both recurrence and recovery. Less than 10% of studies shared a common definition of recurrence. Conclusion. Because of a lack of an agreed terminology it is very difficult to compare results between studies reporting recurrence rates or evaluating strategies to prevent recurrence. Steps to achieve consensus on recurrence and recovery definitions are required. In the interim, it is recommended that a minimum pain duration of 24 hours with a minimum pain intensity equivalent to the appropriate minimal important change for the chosen scale, be used for defining a recurrence. If disability measures are used, it is also recommended that the appropriate minimal important change be used. For recovery, a minimum duration of 1 month pain-free should be used.