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.