OBJECTIVE: To describe the magnitude of patient-reported nonadherence with guideline-recommended care for acute low back pain. DESIGN: Secondary analysis of data from participants enrolled in the Paracetamol for Acute Low Back Pain study trial, a randomized controlled trial evaluating the effectiveness of paracetamol for acute low back pain. SETTING: Primary care, general practitioner. PARTICIPANTS: Data from participants with acute low back pain (N=1643). INTERVENTIONS: Guideline-recommended care, including reassurance, simple analgesia, and the advice to stay active and avoid bed rest. Also, advice against additional treatments and referral for imaging. MAIN OUTCOME MEASURES: Proportion of nonadherence with guideline-recommended care. Nonadherence was defined as (1) failure to consume the advised paracetamol dose, or (2) receipt of additional health care, tests, or medication during the trial treatment period (4wk). Multivariable logistic regression analysis was performed to determine the factors associated with nonadherence. RESULTS: In the first week of treatment, 39.7% of participants were classified as nonadherent. Over the 4-week treatment period, 70.0% were nonadherent, and 57.5% did not complete the advised paracetamol regimen. Higher perceived risk of persistent pain, lower level of disability, and not claiming workers' compensation were associated with nonadherence, with odds ratios ranging from .46 to 1.05. CONCLUSIONS: Adherence to guideline-recommended care for acute low back pain was poor. Most participants do not complete the advised paracetamol regimen. Higher perceived risk of persistence of complaints, lower baseline disability, and participants not claiming workers' compensation were independently associated with nonadherence. CI - Copyright (c) 2017 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.