BACKGROUND: High pre-pregnancy body mass index (BMI) and excessive gestational weight gain (GWG) are suggested to influence risk of asthma and atopic disease in offspring. OBJECTIVE: We examined the effect of BMI and GWG on risk of asthma, wheezing, atopic eczema (AE), and hay fever in children during the first 7 years of life. METHODS: This was a cohort study of 38,874 mother-child pairs from the Danish National Birth Cohort (enrollment 1996-2002) with information from the 16th week of pregnancy and at age 6 months, 18 months, and 7 years of the child. Odds ratios (ORs) with 95% CIs were calculated by logistic regression with adjustment for potential confounders. RESULTS: During the first 7 years of life, 10.4% of children developed doctor-diagnosed asthma, 25.8% AE, and 4.6% hay fever. Maternal BMI and to a lesser extent GWG were associated with doctor-diagnosed asthma ever. In particular, BMI ≥ 35 (adjusted OR, 1.87; 95% CI, 0.95-3.68) and GWG ≥ 25 kg (adjusted OR, 1.97; 95% CI, 1.38-2.83) were associated with current severe asthma at age 7 years. Maternal BMI was also associated with wheezing in offspring, with the strongest association observed between BMI ≥ 35 and late-onset wheezing (adjusted OR, 1.87; 95% CI, 1.28-2.73). Maternal BMI and GWG were not associated with AE or hay fever. CONCLUSIONS: Maternal obesity during pregnancy was associated with increased risk of asthma and wheezing in offspring but not with AE and hay fever, suggesting that pathways may be nonallergic.