Viet Nam's mandatory motorcycle helmet law and its impact on children.

Objective: To measure the use of motorcycle helmets in children and to determine the reasons why children wear helmets less often than adults.

Methods: The frequency of helmet wearing among adults and children was ascertained by trained roadside observers, and randomized road user surveys were completed in four major centres in Viet Nam: Hanoi, Ho Chi Minh City, Can Tho and Da Nang. Survey data on key questions were cross tabulated, and chi2 was calculated for significant differences between parents and non-parents (0.