BACKGROUND: Corticosteroid (CS) treated boys with DMD display higher rates of height stunting, higher weight gain, improved motor function scores and delayed loss of ambulation compared to untreated patients. However, the relationship between growth and motor function has historically been understudied due to modelling complexities. METHODS: In this analysis, we use the newly developed motor function centiles for the NSAA, RFF and 10MWR. We consider each combination of growth (height and weight SD) and motor function using multivariate regression models controlling for differential CS treatment (prednisolone/deflazacort, daily/intermittent). This allows inference on the growth and motor function outcomes separately and on the relationship between the outcomes. RESULTS: We consider 559 steroid-treated boys with DMD between the ages of 5 and 16 over 1643 assessments. Better motor function trajectories were observed in those treated with daily CS, with the deflazacort daily group displaying a positive NSAA centile trajectory (annual change of 0.07 SD). There was a mild, negative pairwise correlation between the annual changes in NSAA and 10MWR Z-Scores, and height and weight Z-Scores, ranging from -0.25 to -0.36. This indicated that patients with a milder weight gain or more severe height stunting trajectory with respect to their CS treatment were more likely to exhibit a more favourable NSAA or 10MWR trajectory over time. CONCLUSIONS: This work describes the complex relationships between motor function, CS treatment and growth and provides insights for conversations about the relative benefits and negative effects of CS.