Objective To assess the composition of lumbar multifidus muscle, in patients with unilateral lumbar disc herniation causing nerve compression, using quantitative and qualitative magnetic resonance imaging (MRI) measurement methods. Methods Two radiologists retrospectively measured MRI signal intensity of the multifidus muscle, as high intensity represents more fat, and visually graded the fat content using a 5-point grading system in patients with unilateral subarticular lumbar disc herniation. Findings from the herniated and contralateral sides were compared. The association between fat content and severity of nerve compression and symptom duration were also evaluated. Results Ninety patients (aged 24-70 years) were included. Signal intensity of the affected multifidus muscle was significantly higher versus the contralateral muscle for quantitative measurements and qualitative scoring for both investigators. Significant correlations were observed between the severity of nerve compression and symptom duration and the degree of fat content in the affected multifidus muscle. Conclusions Higher fat composition was observed in the multifidus muscle ipsilateral to the lumbar disc herniation versus the contralateral side. Straightforward visual grading of muscle composition regarding fat infiltration appeared to be as useful as quantitative measurement.