Objective: To characterize the measurement scales and levels of psychological distress reported among published studies of acute low back pain (LBP) in the scientific literature. Data Sources: Peer-reviewed scientific literature found in 8 citation index search engines (CINAHL, Embase, MANTIS, PsycINFO, PubMed, Web of Science, AMED, and Academic Search Premier) for the period from January 1, 1966, to April 30, 2015, in English, Danish, Norwegian, and Swedish languages. Study Selection: Cross-sectional, case-control, cohort, or randomized controlled trials assessing psychological distress and including participants drawn from patients and workers (or an identifiable subset) with acute LBP (<8wk). Three researchers independently screened titles, abstracts, and full-length articles to identify peer-reviewed studies according to established eligibility criteria. Data Extraction: Descriptive data (study populations, definitions of LBP, distress measures) were systematically extracted and reviewed for risk of bias. Distress measures were described, and data were pooled in cases of identical measures. Reported levels of distress were contextualized using available population norms, clinical comparison groups, and established clinical cutoff scores. Data Synthesis: Of 10,876 unique records, 23 articles (17 studies) were included. The most common measures were the Beck Depression Inventory, the modified version of the Zung Self-Rated Depression Scale, the Center for Epidemiologic Studies-Depression Scale, and the Medical Outcomes Study 12-Item Short-Form Health Survey and Medical Outcomes Study 36-Item Short-Form Health Survey. Pooled results for these scales showed consistent elevations in depression, but not anxiety, and reduced mental health status in comparison with the general population. Conclusions: Based on the high consistency across studies using valid measures with a low to moderate risk of bias, there is strong evidence that psychological distress is elevated in acute LBP. (C) 2016 by the American Congress of Rehabilitation Medicine