Objective : To assess agreement in detection lumbar disc herniation between limited and full protocol MRI. Design : Equivalence study and diagnostic cross-sectional study. Setting :Department of Radiology Faculty of Medicine Siriraj Hospital. Method :One hundred and twenty three patients requested lumbar spine MRI for diagnosis of disc herniation were assessed for the severity and duration of the low back pain. The routine full protocol MRI was performed in each patient, which was composed of sagittal T1-weighted image, sagittal T2-weighted image and axial T2-weighted image. The sagittal T2-weighted image was selected as the limited protocol MRI. The limited protocol and full protocol MRI of each patient were separately interpreted by three neuroradiologists to assess disc herniation and nerve root compression. The consensus results of findings of limited and full protocol were compared. The diagnostic performance of each protocol was analyzed using surgery as the gold standard. Then the diagnostic statistics of both protocols were compared. Result : There were 123 patients (62 females, 61 males) enrolled into the study with range of age of 21-60 years old (means = 42.91). The duration of pain before MRI examination was ranged from 1-204 months (mean = 31.20 months). The degree of severity was mild in 23.58%, moderate 45.52% and severe 30.89% of cases. Thirty-three cases were operated and the rest were conservatively treated. For detection of lumbar disc herniation (LDH), the limited protocol MRI gave the interpretation results equally to full protocol MRI (theta = 1.04, 95%CI=0.94,1.14 with accepted range of 0.95-1.05). In nerve root compression, the limited protocol was not equal to full protocol MRI theta= 0.75, 95%CI=0.87,0.63). The sensitivity, specificity, accuracy, PPV, NPV, and LR+ in the surgical group of limited protocol in diagnosis of LDH were 82.61%, 80%, 81.82%, 90.48%, 60.67%, 4.13 respectively. The same results for limited protocol in nerve root compression were 54.84%, 100%, 57.58%, 100%, 12.5%. The sensitivity, specificity, accuracy, PPV, NPV and LR+ of full protocol MRI in diagnosis of LDH were 82.61%, 70%, 78.79%, 86.36%, 63.64%, 2.75 and of nerve root compression were 80.65%, 100%, 81.82%, 100%, 25% respectively. The sensitivity and specificity in diagnosis of LDH were not different in both protocols but the sensitivity of nerve root compression was statistically different (p<0.013, 95%CI = -0.33, -0.25). The author concluded that limited protocol MRI may replace full protocol MRI in diagnosis of LDH for patients suspected LDH whom MRI were requested but not in nerve root compression.