Acute and chronic headache attributed to whiplash injury are new diagnostic entities in the International Classification of Headache Disorders, second edition. A main objective of the present study was to assess the validity of these nosologic entities by studying the headache pattern in an inception cohort of 210 rear-end car collision victims and in 210 matched controls. Consecutive drivers involved in rear-end collisions were identified from the daily records of the Traffic Police Department of Kaunas, Lithuania. A standard self-report questionnaire was sent to the drivers between 2 and 7 days after the collision, and their passengers were recruited as well. Headache and neck pain were evaluated within 7 days of the collision, at 2 months and 1 year after the collision. A control group of non-traumatized subjects received questionnaires at the time of the selection and 1 year later. Of the 75 collision victims who developed headache within the first 7 days of the collision, 37 had a clinical picture in accordance with the criteria for acute whiplash headache (i.e., concomitant neck pain) and 38 did not. For acute headache after collision, concomitant neck pain was of no relevance to the headache type or its course. In both these subgroups, migraine and tension-type headache could be diagnosed in similar proportions and the prognosis after 2 months and 1 year was also similar. Preexisting headache was a strong prognostic factor in both groups for both acute and chronic pain. Compared with the non-traumatized control group, the 1-year incidence of new or worsened headache, or of headache improvement, was the same. A likely interpretation of the data is that acute headaches after rear-end car collisions mainly represent episodes of a primary headache precipitated by the stress of the situation. We conclude that the nosologic validity of both acute and chronic whiplash headache is poor as the headaches, in accordance with the criteria lack distinguishing clinical features and have the same prognosis compared with headaches in a control group.