Pars interarticularis stress injury and spondylolysis are frequent causes of back pain among young athletes. Accurate diagnosis and grading of these conditions are essential to institute appropriate management strategies in order to achieve optimal outcomes. The aim of management strategies for acute active spondylolysis stress reactions and stress fractures is to achieve bone healing while avoiding recurrence and non-union, with the ultimate goal of returning to sports as determined by symptom resolution. Although various radiological classification systems for spondylolysis have been described, their application for prognostication and surveillance has been limited. The development of a standardised, validated classification system that guides management decisions and predicts healing outcomes would immensely benefit radiologists and clinicians. This article reviews the current imaging recommendations for diagnosing and grading pars stress injuries and spondylolysis before proposal of a novel radiological classification system. The system utilises standard MRI sagittal sequences with clear inter- and intra-observer agreement. We aim to validate the classification system through interrogation of the injury, clinical and return-to-play data in young athletes, with an aim to determine early prognostic accuracy of pars stress injuries.