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Abstract Introduction: There are different methods for measuring the angle of lumbar lordosis. This study investigated a comparison between the angles of lumbar lordosis in clinical method using flexible ruler with that of radiograms. The accuracy level of these two applied methods was a goal of this research. Materials & methods: This analytic cross-sectional study was conducted in Zahedan University of Medical Sciences. One hundred-twelve patients with low back pain, who had lumbar lateral radiograms, were conveniently recruited from the physical therapy clinics. The angle of lumbar lordosis (degree) was measured twice using Cobb’s principle on lumbar lateral radiograms and clinically using a flexible ruler. The obtained data was analyzed using descriptive statistics and Pearson Correlation test. Findings: The mean age of participants was 31.6±9 years. The mean angle of lumbar lordosis on clinical and radiographic methods was 36.0±9.7 degrees and 38.5±9.4 degrees, respectively. The mean angle of lumbar lordosis measured in Cobb’s method were significantly correlated (r=0.95) with the mean angle of lumbar lordosis measured in flexible ruler (P<0.0001). Conclusion: The results showed that lumbar lateral radiograms were reliable tools for measuring the angle of lumbar lordosis.