Background Previous studies suggest that a greater proportion of neck injury patients, whose injuries were sustained through whiplash accidents, become chronic due to a component of sickness-focusing. However, it is also possible that some of those with neck injuries were already more frail prior to the injury, resulting in more consequences from a certain intensity of injury. The objective of this study was to compare co-morbidity and mortality in people with a registered neck injury diagnosis, evaluated prior to and after the neck injury, to people without a registered neck injury evaluated at the same time-points. Methods From a hospital patient registry over a 12-year period, we identified those with the diagnosis ‘cervical-column distortion’ and matched four controls for each of them on sex, age, marital status and county of residence. For calculations of co-morbidity, those with an injury at year 1, who thus had no prior data, and for those at year 12 who did not have post data, were not included. The same applied to their individually matched controls. Health data for up to 3 years prior to and up to 3 years after the year of injury were recorded. Results We identified 94,224 cases and 373,341 controls. Those with registered neck injuries had 1.2-2.0 times more co-morbidities than controls after the injury, but had already had about the same (1.3-1.8 more co-morbidities) number of co-morbidities prior to the injury. Mortality up to 12 years was approximately the same in the two groups. Conclusions Those people having a registered neck injury had more co-morbidity diagnoses both before and after the injury than those without a registered neck injury. This suggests that the co-morbidities observed after the injury may be partly related to already existing general high health care-seeking and/or a low health status, rather than being entirely the consequence of the injury.