A 7-year-old boy travelling in the rear seat of a sedan car was wearing a lap-shoulder seat belt and sitting on a booster seat. Following a collision the boy 'submarined' under the seat belt sustaining trauma to the anterior aspect of his neck, cardiac arrest and subsequent death from hypoxic-ischaemic encephalopathy. This case demonstrates a potential problem with unsecured older-style booster seats. Movement of a seat in a collision may cause a child to slip under a seat belt and sustain significant neck injuries. Seatbelts for children must be correctly fitted, booster seats or capsules must be securely fastened and manufacturer's recommendations for size and weight limits should be followed. Unfortunately older booster seats may not have attached instructions for installation and use, may not fit later model vehicles, may not conform to current safety recommendations and may have worn webbing. For these reasons their use should be discouraged.