The objective of this study was to determine whether birth order is associated with total or cause-specific adult mortality and whether the association differed by sex, was confounded by age, number of siblings, or socioeconomic status, or was mediated by personality, education, or health behaviors. Teachers throughout California identified intellectually gifted children as part of a prospective study begun in the 1920s by Lewis Terman. Information on birth order was available on 1162 subjects (85% of cohort) who have since been followed for over 70 years. Cox proportional hazards models indicated that birth order was not associated with adult all-cause, cardiovascular, or cancer mortality. Among women, middle children were more likely than oldest children to die from causes of death other than cardiovascular disease or cancer, although the numbers in this category were small. This study did not provide evidence that birth order is associated with adult mortality in this highly intelligent, middle-class cohort.