Some studies indicate that children born to younger mothers are at higher risk tor wheezing or asthma. I conducted a case-control study that included 457 new cases of asthma in 3-and 4-year-old children and an equal number of controls. I found that, in comparison with children of mothers 30 years of age or older, children of mothers age 26–30 years had an adjusted odds ratio (OR) of 1.16 [95% confidence interval (CI) = 0.73–1.85] of developing asthma; children of mothers between 21 and 25 years of age had an OR of 1.25 (95% CI = 0.76–2.07), and those whose mothers were 20 years of age or younger had an OR of 3.48 (95% CI = 1.08–11.22).