Introduction: Low back pain is a common problem of modern society. Reliable functional diagnosis is the key to diagnosis and is the first step in treating this disease and to prevent its recurrence. The aim of the study was to examine the inter- rater reliability of diagnosis by a novice therapist after completing the course “A” of the McKenzie method compared with the diagnosis made by the experienced instructor. Material and methods: The study was conducted at the Institute McKenzie Poland in Poznan. Patients (n = 30) of the low back pain were diagnosed by McKenzie method. Following variables were analyzed: diagnosis, directional, starting position for the exercise and their frequency. Results: Following inter-rater reliability was found for Kappa coefficient: diagnosis 0.75, therapeutic direction 1.0, starting position 1.0 and frequency of exercise 0.78. Conclusions: 1. Course “A” of McKenzie method can fully prepare the therapist for tasks such as diagnosis and treatment planning of patients with low back pain. 2. McKenzie method allowed to minimize diagnostic errors, despite the large difference in the experience of diagnosticians. 3. Differences arising from the experience of diagnosticians were primarily in situations diagnose patients eligible for “other”.