Lumbar disc herniation (LDH) is rare in juveniles. LDH occurring at age 20 years or younger is referred to as juvenile disc herniation (JDH). While adult LDH is regarded as an advanced stage of disc degeneration, it remains unclear why intervertebral discs rupture in youth. This study aimed to characterize magnetic resonance imaging (MRI) findings of JDH and investigate possible etiological factors. From 2013 to 2020, JDH patients and controls were identified and interviewed to assess demographics, general lifestyles, and family histories. MRIs were evaluated for disc degeneration, epiphyseal ring separation, Modic changes and endplate lesions. The relationships between JDH and suspected risk factors were examined. A total of 297 JDH patients (199 boys and 98 girls, age 17.3 ± 2.1 years) and 185 controls (age 17.1 ± 2.4 years) were studied. Age, body mass index, exposures to daily physical labor, regular exercise, and daily sitting time were similar between JDH cases and controls. A family medical history of serious back pain was more common in JDH patients than in controls (59.4% vs. 26.5%, p < 0.001), as well as family history of clinically established LDH (45.0% vs. 12.4%, p < 0.001). Epiphyseal ring separation was identified in 102 (29.2%) herniated discs in 91 (36.4%) JDH patients, while occurring in only 5 (1.4%) control participants (p < 0.001). Overall, severe disc degeneration was not a prominent finding in JDH patients. In conclusion, epiphyseal ring separation was a common magnetic resonance feature in JDH. Findings suggest a genetically mediated developmental model of JDH, rather than a model of premature disc degeneration.