BACKGROUND: Osgood Schlatter Disease (OSD) is a common injury in adolescents. A recent systematic review identified multiple tissue characteristics evaluated in imaging studies, but the studies used different imaging modalities, used varying MRI protocols and were of poor study quality, which led to conflicting findings and hamper the clinical utility of MRI scans. This study aimed to develop and evaluate the reliability of a semi-quantitative MRI scoring system for use in adolescents with OSD. MATERIALS AND METHODS: Based on a systematic review, we used an expert-led process to develop a scoring list to describe soft tissues, cartilage, bone, and morphometric characteristics in adolescents with OSD. 1.5 T MRI was performed on the most symptomatic knee in adolescents with OSD. A trained radiologist and a research trainee each assessed 10 cases twice to assess the intra- and inter-rater reliability of the scoring list. RESULTS: The final 18 item scoring list included an assessment of the patellar tendon, infrapatellar bursa, cartilage, and the tibial epiphysis, metaphysis, and tibial tuberosity, which were scored by signal intensity, degree, and signal homogeneity. Patellar height, patella morphology, patellar tendon attachment, and tendon thickness and width were quantified. Ten adolescents with OSD (13.2 ± 1.1, 30 % female) were included for reliability. Most features showed good to very good (κ and ICC > 0.6) reliability. The exceptions were intra-rater reliability for superficial bursa homogeneity (κ = 0.51) and inter-rater reliability for signal degree in the patellar tendon (κ = 0.55), tibial epiphysis (κ = 0.53) and tibial tuberosity (κ = 0.52) and patella morphology ratio (ICC: -0.16, p = 0.67. Reliability for patella height and patellar tendon width had the highest reliability (intra-rater ICC (0.75-0.98); inter-rater ICC (0.48-0.93)). CONCLUSION: This semi-quantitative scoring system for MRI allows the comprehensive and reliable assessment of features relevant for evaluating affected tissues in adolescent patients with OSD.