In past time no significant standards have been applied to the qualification of bicycle safety helmets. As a result, a wide variety of headgear has become available for bicycle riders, who surely have expectations of protection by the use of such equipment. With the issuanCe of the industry consensus standard, ANSI Z-90.4, 1984, a minimum performance standard for bicycle safety helmets has been established. Laboratory tests confirm the fundamental principles of protective headgear and illustrate that both satisfactory and unsatisfactory helmet designs are available to the uninformed consumer. However, compliance with the new ANSI Z-90.4 standard assures acceptable impact attenuation in typical accidents.