Objectives: To investigate the effectiveness of botulinum toxin in preventing the development of chronic whiplash-associated disorder. Design: Prospective, randomized, placebo-controlled double-blind study. Setting: Regional Neurological Rehabilitation Centre with participants being at home. Subjects: Thirty-seven patients with whiplash-associated disorder who remained symptomatic two months after injury. Interventions: Patients were randomized to receive either 250 units botulinum toxin type A (Dysport) or placebo (normal saline). Four trigger points were injected with 0.625 mL of injectant. Outcome measures: Tenderness to palpation scores, visual analogue pain scale, Vernon—Mior Neck Pain and Disability Index and cervical range of motion. Follow-up assessments were carried out at four weeks and three months after treatment. Results: Twenty participants received botulinum toxin and 17 received placebo. Both groups showed a tendency towards improvement in pain scores, Vernon—Mior Index and range of motion at four weeks and three months, with the changes being more pronounced in the toxin group. The change in Vernon—Mior Index in the toxin group was both statistically and clinically significant (i.e. a change of score of ≥5 from baseline to follow-up). Group comparisons did not meet statistical significance. Conclusion: The improvements in outcome measures suggest that botulinum toxin type A may have a role to play in the management of whiplash-associated disorder but larger studies are required to clarify the situation.