Background Urban bicycle couriers may have a high incidence of injuries. Most messengers work as contractors and hence their injuries are not well documented. Methods To quantify injury rates and severity among urban bicycle couriers a convenience sample of 113 couriers in the city of Boston completed a two-page self-administered survey. Results Most working couriers have suffered at least one injury resulting either in days lost from work (70%) and in visits to a health-care professional or hospital (55%). The annual incidence rate for injuries resulting in days away from work was 47/100-bike couriers. Bone fractures accounted for the most days lost from work, followed by dislocations, sprains, and strains. Collisions and avoiding collisions with motor vehicles, including being "doored," and collisions with pedestrians accounted for the majority (66%) of events leading to injury. Twenty-four percent of messengers reported wearing a helmet on a regular basis, and 32% have health insurance. Conclusions Urban bicycle messengers are a poorly documented, largely unstudied workforce who suffer a very high rate of occupational injury. (C) 2002 Wiley-Liss, Inc.