To examine the secular trends of mortality from motor vehicle crashes, the authors compiled annual population and mortality data for the United States from 1910 to 1994 and performed an age-period-cohort analysis through graphical presentation, median polish, and Poisson regression modeling. During the 85-year study period, death rates from motor vehicle crashes showed two peaks, first in 1935-39 and then in 1965-69. Age and period effects accounted for 94% of the variation in motor vehicle mortality in men and 84% of the variation in women. Age patterns of motor vehicle mortality varied greatly with birth cohorts: for those who were born before 1910, death rates increased with age; for those born after 1910, death rates peaked at age 20-24 years for men and at age 15-19 years for women. A crossover characterized by a downward trend in death rates among the elderly and an upward trend among adolescents and young adults was observed in both sexes. The complex age, period, and cohort patterns of motor vehicle mortality are likely to have been shaped by changes in traffic patterns and driver behavior, and by improvements in safety design and emergency medical service systems.