All too often I see people riding their beloved bikes without their trustworthy helmets. I know the feel of wind in your hair is great, but check out these figures from A Case-Control Study of the Effectiveness of Bicycle Safety Helmets:
Of the 99 cyclists with serious brain injury only 4 percent wore helmets. In regression analyses to control for age, sex, income, education, cycling experience, and the severity of the accident, we found that riders with helmets had an 85 percent reduction in their risk of head injury (odds ratio, 0.15; 95 percent confidence interval, 0.07 to 0.29) and an 88 percent reduction in their risk of brain injury (odds ratio, 0.12; 95 percent confidence interval, 0.04 to 0.40).
We conclude that bicycle safety helmets are highly effective in preventing head injury. Helmets are particularly important for children, since they suffer the majority of serious head injuries from bicycling accidents. (N Engl J Med 1989;320:1361–7.)
Makes you want to grab that helmet.