Objective: To determine the absolute and relative reliability of intra-observer and interobserver measurements of postural balance using the One Leg Stand Test in patients with low back pain. Patients and methods: Forty-eight patients with chronic low back pain advised to do exercise were included. A test protocol was established based on review of the literature and a pilot test. Patients were timed for their ability to stand on one leg with their eyes open and with eyes closed. After a 20-min break, the procedure was repeated to check for reproducibility.Results: Eyes open: a ceiling effect was seen as more than 48% of patients were able to stand for the maximum time, and no further analysis was done. Eyes closed: intra-observer reliability was tested in 21 patients; absolute reliability showed a standard error of the measurement (SEM) of 2.48 s and a minimal detectable change (MDC) of 6.88. The relative reliability was acceptable with an intra class correlation coefficient (ICC) of 0.86. Interobserver reliability was tested in 27 patients; absolute reliability showed a SEM of 1.42 s and a MDC of 3.95. The relative reliability was acceptable with an ICC of 0.91. Conclusions: The One Leg Stand Test can be used to test postural balance in patients with chronic low back pain, as the reliability of the test was acceptable.