Recent data show that maternal smoking during pregnancy adversely affect respiratory function in newborn infants (Lancet 1996;348:1060-4). An important interaction has been previously demonstrated between early lung function and symptoms of asthma in later childhood. The aim of the present study was therefore to examine whether in utero smoke exposure is associated with asthma at age 17. Data regarding parental smoking during pregnancy was obtained by postpartum interview from 16,239 infants born in Jerusalem between November 1974 and December 1977. Additional Perinatal data was available from the computerized files of the Jerusalem Perinatal Study. The incidence of asthma was significantly higher (p<0.001) for females born to mothers who smoked during pregnancy 3.4% (42/1246) vs. 1.7% (110/6593). A similar difference was not observed for males 4.5% (57/1266) vs. 4.2%(301/7134). Paternal smoking was not associated with asthma in both females, 2.0% (69/3427) vs. 1.9% (83/4412), and males, 3.9% (139/3531) vs. 4.5%(219/4869). A multiple logistic regression was used to estimate the odds ratio for developing asthma by age 17. The odds ratios for asthma among female infants whose mothers smoked during pregnancy, after adjusting for the confounding effect of maternal ethnic origin, age, social class, education, preeclampsia, birth weight, gestational age, and birth order was 1.67 (95% confidence interval 1.11 - 2.53). We conclude that the previously described adverse affect of smoke exposure on lung development in utero may have long-term effects extending to late adolescence.