OBJECTIVE To assess the effectiveness of helmets in preventing facial injuries. METHODS Case-control study between March 1, 1992, and August 31, 1994. METHODS Seven Seattle, Wash, area hospitals including the regional trauma center and a large staff-model health maintenance organization. METHODS Cases were patients with serious facial injury, ie, fractures or lacerations; controls were patients who had injuries other than facial. Minor facial injuries were excluded to avoid ascertainment bias in those seeking care for serious injuries to other areas. RESULTS Serious facial injuries occurred to 700 (20.7%) patients. Helmets were used by 47% of cases and 57% of controls. After adjusting for age, sex, speed, and surface, we found that helmets reduced the risk of injury to the upper face (odds ratio [OR], 0.36; 95% confidence interval [CI], 0.26-0.49) and middle face (OR, 0.35; 95% CI, 0.24-0.50) but had no significant effect on serious injury to the lower face (OR, 0.88; 95% CI, 0.72-1.07). CONCLUSIONS Bicycle helmets offer substantial protection for the upper and mid face in addition to their known protection against head injuries. Helmets do not appear to offer any protection for the lower face.