Traumatic spinal cord injury can result in severe motor and sensory impairment. Accumulating evidence suggests that traumatic spinal cord injury triggers a systemic immune response involving circulating immunocytes. We sought to investigate the circulating immunocytes composition during the acute phases of spinal cord injury and its association with clinical parameters. Flow cytometry was used to perform detailed immunoassays in spinal cord injury mice and patients with acute disease. We found that the frequencies of circulating immunocytes were significantly different among mice with different baseline degrees of injury severity. Moreover, the severity of injury in human spinal cord injury patients was found to be positively correlated with neutrophil counts and the proportion of cluster of differentiation 8(+) T cells in the acute phase but inversely correlated with lymphocytes, cluster of differentiation 4(+) T cells and the cluster of differentiation 4+/cluster of differentiation 8(+) T-cell ratio. In addition, multivariate analysis revealed that acute spinal cord injury induced increases in neutrophils (odds ratio 1.215, 95 % confidence interval=1.005-1.468), lymphocytes (odds ratio=28.208, 95 % confidence interval=2.190-363.390) and cluster of differentiation 8+ T cells (odds ratio=1.186, 95 % confidence interval=1.033-1.362) were independent predictors of association impairment scale grade conversion failure and the predictive model displayed robust sensitivity (88.0 %) and specificity (88.2 %). Our findings not only elucidate the association between early circulating immune cells and injury severity, but also indicate the prognostic value of modeling early circulating neutrophil and lymphocyte counts with proportions of cluster of differentiation 8(+) T cells for predicting association impairment scale grade conversion at 6 mo post spinal cord injury.