Traffic safety mandates are typically designed to reduce the harmful externalities of risky behaviors. We consider whether motorcycle helmet laws also reduce a beneficial externality by decreasing the supply of viable organ donors. Our central estimates show that organ donations resulting from fatal motor vehicle accidents increase by 10 percent when states repeal helmet laws. Two features of this association suggest that it is causal: first, nearly all of it is concentrated among men, who account for over 90 percent of all motorcyclist deaths, and second, helmet laws are unrelated to the supply of donors who die in circumstances other than motor vehicle accidents. The estimates imply that every death of a helmetless motorcyclist prevents or delays as many as .33 death among individuals on organ transplant waiting lists.