Study Design A retrospective review of prospectively evaluated magnetic resonance (MR) images. Purpose Routine lumbar axial and sagittal MR images may not clearly demonstrate nerve root anomalies and entrapments in the extraforaminal region. Thus, lumbar extraforaminal lesions or nerve root anomalies may be underdiagnosed because of unfamiliar radiological anatomy. We aimed to investigate the clinical efficacy of our oblique magnetic resonance imaging (MRI) technique for diagnosing nerve root anomalies and entrapment lesions. Overview of Literature Evaluation of clinical usefulness of oblique lumbar MRI for nerve root anomalies and extraforaminal entrapment lesions. Methods In total, 162 patients (60 males and 102 females; mean age, 59.8±17.8 years) with suspected nerve root anomalies and entrapments in routine axial and sagittal MR images underwent unilateral or bilateral oblique lumbar T2-weighted MRI. The axial angle of the oblique image was parallel to the foramen. The oblique MRI findings of the symptomatic side were compared with those of the asymptomatic side in cases with unilateral pathologic lesions. Interobserver agreement was analyzed using kappa statistics. Results The following abnormal findings were obtained: nerve root entrapment due to foraminal stenosis in 82 cases; extraforaminal disk herniation in 29; conjoined nerve root in six; and foraminal bony cyst in one. Forty-three of the 46 patients experienced unilateral lateralizing symptoms, unilateral nerve root entrapment due to foraminal stenosis, herniated disk, and extraforaminal bony cyst compared with the asymptomatic contralateral side (p <0.05). Conclusions Our results suggest that oblique lumbar MRI is a simple and valuable modality for diagnosing anomalous lumbar nerve root lesions and entrapment.