Prenatal exposure to cigarettes and familial risk group were jointly evaluated to determine their influence on Body Mass Index (BMI) during three developmental periods (ages 8–11, 12–15, and 16–18). Asterisks indicate a significant difference. For the 8–11-year-old low-risk offspring, t =2.83, df =36, P =0.008; for the 12–15-year-olds, t =2.97, df =8.9, P =0.02; for the 16–18-year-olds, t =2.61, df =9.3, P =0.03. There were no significant differences in BMI by prenatal exposure to cigarettes that could be detected in the high-risk offspring.