Summary Background Traumatic spinal cord injury is a serious disorder in which early prediction of ambulation is important to counsel patients and to plan rehabilitation. We developed a reliable, validated prediction rule to assess a patient's chances of walking independently after such injury. Methods We undertook a longitudinal cohort study of adult patients with traumatic spinal cord injury, with early (within the first 15 days after injury) and late (1-year follow-up) clinical examinations, who were admitted to one of 19 European centres between July, 2001, and June, 2008. A clinical prediction rule based on age and neurological variables was derived from the international standards for neurological classification of spinal cord injury with a multivariate logistic regression model. Primary outcome measure 1 year after injury was independent indoor walking based on the Spinal Cord Independence Measure. Model performances were quantified with respect to discrimination (area under receiver-operating-characteristics curve AUC). Temporal validation was done in a second group of patients from July, 2008, to December, 2009. Findings Of 1442 patients with spinal cord injury, 492 had available outcome measures. A combination of age (<65 vs ≥65 years), motor scores of the quadriceps femoris (L3), gastrocsoleus (S1) muscles, and light touch sensation of dermatomes L3 and S1 showed excellent discrimination in distinguishing independent walkers from dependent walkers and non-walkers (AUC 0·956, 95% CI 0·936–0·976, p<0·0001). Temporal validation in 99 patients confirmed excellent discriminating ability of the prediction rule (AUC 0·967, 0·939–0·995, p<0·0001). Interpretation Our prediction rule, including age and four neurological tests, can give an early prognosis of an individual's ability to walk after traumatic spinal cord injury, which can be used to set rehabilitation goals and might improve the ability to stratify patients in interventional trials. Funding Internationale Stiftung für Forschung in Paraplegie.