A dramatic decline in walking and cycling to school has been observed in many geographic and cultural regions, and most children in the US are now driven to school in private vehicles. There are a number of health implications associated with the choice of commute mode, including traffic safety, exposure to air pollution, and levels of physical activity and obesity, and the risks and benefits of each must be weighed. This paper reviews current evidence on these risks and benefits for each health topic area. From a traffic safety perspective, buses are best, while the risks of private vehicle and walking are roughly comparable. Less apparent is the observation that one student’s travel choice will affect another student’s risk, because changes in mode share alter the overall risk profile. Walking to school has been associated with higher levels of physical activity, although it is unclear whether this association is causal, or merely reflects a preference for walking among active children. Current evidence does not support a link between walking to school and reduced body-mass index or levels of obesity. A discussion of concurrent health effects in all areas has implications both for programs promoting walking to school and for individuals choosing among commute modes.