There is a lack of studies examining whether mechanism-based classification systems (CS) acknowledging biological, psychological and social dimensions of long-lasting low back pain (LBP) disorders can be performed in a reliable manner. The purpose of this paper was to examine the inter-tester reliability of clinicians' ability to independently classify patients with non-specific LBP (NSLBP), utilising a mechanism-based classification method. Twenty-six patients with NSLBP underwent an interview and full physical examination by four different physiotherapists. Percentage agreement and Kappa coefficients were calculated for six different levels of decision making. For levels 1-4, percentage agreement had a mean of 96% (range 75-100%). For the primary direction of provocation Kappa and percentage agreement had a mean between the four testers of 0.82 (range 0.66-0.90) and 86% (range 73-92%) respectively. At the final decision making level, the scores for detecting psychosocial influence gave a mean Kappa coefficient of 0.65 (range 0.57-0.74) and 87% (range 85-92%). The findings suggest that the inter-tester reliability of the system is moderate to substantial for a range of patients within the NSLBP population in line with previous research.