Study design Retrospective case series Setting Three hospitals in China. Objective Previous research indicates that only neurological status on admission determines prognosis of acute hyperextension myelopathy (AHM). The object of this study is to analyze other unfavorable predictors of AHM in children. Methods The clinical data of children with AHM were retrospectively analyzed. The ASIA impairment scale (AIS) grade was recorded upon admission and at last follow-up. Intramedullary lesion length (IMLL) was measured in the sagittal T2-weighted imaging (T2WI) within two weeks after onset; gadolinium enhancement in the cord was recorded for each patient. Relationships among AIS grade, IMLL, gadolinium enhancement in the cord, and clinical improvement were assessed. Results A total of 33 patients were included in this retrospective study. IMLL between complete and incomplete injury was significantly different (p < 0.01) in the subacute stage, and no difference was observed in the acute stage. Correlation analysis revealed that AIS grade on admission (r = 0.906, p < 0.001) was significantly positively correlated with clinical improvement. IMLL (r = -0.608, p < 0.001) and abnormal gadolinium enhancement (r = -0.816, p < 0.001) in the cord in the subacute stage were significantly negatively correlated with clinical improvement. There were no associations between IMLL in the acute stage and clinical improvement (r = -0.248, p = 0.242). The statistically significant predictors of clinical improvement were AIS grade on admission, IMLL in the subacute stage, and abnormal gadolinium enhancement. Conclusion IMLL in the subacute stage and abnormal gadolinium enhancement in the cord are two other prognostic predictors of AHM in children.