An evaluation of forty-five athletes who had had an episode of transient neurapraxia of the cervical spinal cord revealed a consistent finding of developmental narrowing of the cervical spinal canal. The purpose of the present epidemiological study was to determine the relationship, if any, between a developmentally narrowed cervical canal and reversible and irreversible injury of the cervical cord with use of various cohorts of football players as well as a large control group. Cohort I comprised college football players who were asymptomatic and had no known history of transient neurapraxia of the cervical cord. Cohort II consisted of professional football players who also were asymptomatic and had no known history of transient neurapraxia of the cervical cord. Cohort III was a group of high-school, college, and professional football players who had had at least one episode of transient neurapraxia of the cervical cord. Cohort IV comprised individuals who were permanently quadriplegic as a result of an injury while playing high-school or college football. Cohort V consisted of a control group of male subjects who were non-athletes and had no history of a major injury of the cervical spine, an episode of transient neurapraxia, or neurological symptoms. The mean and standard deviation of the diameter of the spinal canal, the diameter of the vertebral body, and the ratio of the diameter of the spinal canal to that of the vertebral body were determined for the third through sixth cervical levels on the radiographs for each cohort. In addition, the sensitivity, specificity, and positive predictive value of a ratio of the diameter of the spinal canal to that of the vertebral body of 0.80 or less was evaluated. The findings of the present study demonstrated that a ratio of 0.80 or less had a high sensitivity (93 per cent) for transient neurapraxia. The findings also support the concept that symptoms may result from a transient reversible deformation of the spinal cord in a developmentally narrowed osseous canal. The low positive predictive value of the ratio (0.2 per cent) however, precludes its use as a screening mechanism for determining the suitability of an athlete for participation in contact sports. Developmental narrowing of the cervical canal in a stable spine does not appear to predispose an individual to permanent catastrophic neurological injury and therefore should not preclude an athlete from participation in contact sports.