Objective: To evaluate the effect of pre-injury physical fitness on the initial severity and recovery of motor vehicle-induced neck injury (whiplash injury). Design: A quantitative experimental design using both retrospective and prospective data. Setting: Metropolitan Police physiotherapy and rehabilitation department in the UK. Subjects: One-hundred and two patients with neck pain following whiplash injury. Interventions: Patients were divided into three groups based on pre-injury physical fitness (low, medium and high). Recovery was compared between the three groups initially then again at three and six months. Main measures: Three measurement scales were used: the Neck Disability Index, the Problem Percentage, and the Physical Activity Scale. Results: Pre-injury physical fitness had a marked effect on recovery at three and six months, with the medium and high fitness groups having significantly better recovery than the low fitness group. At three months the Neck Disability Index score for the low fitness group was 12 compared with 7 and 7.5 for the medium and high fitness groups respectively (P = 0.009). At six months the Neck Disability Index score was 9 for the low fitness group compared with 0 and 3 for the medium and high fitness groups (P = 0.002). In addition, the return to work rate was almost twice as high for individuals with medium/high fitness. Conclusion: Early recovery from whiplash injury was significantly more likely for individuals with medium to high levels of pre-injury physical fitness than for individuals with low levels of pre-injury physical fitness.