Mechanisms-based classifications of pain have been advocated for their potential to aid understanding of clinical presentations of pain and improve clinical outcomes. However, the reliability of mechanisms-based classifications of pain and the clinical criteria upon which such classifications are based are not known. The purpose of this investigation was to assess the inter-and intra-examiner reliability of clinical judgments associated with: (i) mechanisms-based classifications of pain; and (ii) the identification and interpretation of individual symptoms and signs from a Delphi-derived expert consensus list of clinical criteria associated with mechanisms-based classifications of pain in patients with low back (±leg) pain disorders. The inter-and intra-examiner reliability of an examination protocol performed by two physiotherapists on two separate cohorts of 40 patients was assessed. Data were analysed using kappa and percentage of agreement values. Inter-and intra-examiner agreement associated with clinicians' mechanisms-based classifications of low back (±leg) pain was 'substantial' (kappa =0.77; 95% confidence interval (CI): 0.57-0.96; % agreement =87.5) and 'almost perfect' (kappa =0.96; 95% CI: 0.92-1.00; % agreement =92.5), respectively. Sixty-eight and 95% of items on the clinical criteria checklist demonstrated clinically acceptable (kappa ≥ 0.61 or % agreement ≥ 80%) inter-and intra-examiner reliability, respectively. The results of this study provide preliminary evidence supporting the reliability of clinical judgments associated with mechanisms-based classifications of pain in patients with low back (±leg) pain disorders. The reliability of mechanisms-based classifications of pain should be investigated using larger samples of patients and multiple independent examiners. © 2010 Maney Publishing.