Introduction Obesity is common among women of childbearing age; intrauterine exposure to maternal obesity or gestational weight gain may influence the development of asthma in early childhood. We examined the relationships of maternal obesity and gestational weight gain with asthma in offspring. Methods We used data from the Early Childhood Longitudinal Study–Birth Cohort, which has a nationally representative sample of children followed from birth in 2001 through age 4 (n = 6,450). Asthma was based on parental report of a medical professional’s diagnosis. We used generalized estimating equation binomial models to compute adjusted odds ratios (ORs) of childhood asthma with maternal obesity and 4 measures of gestational weight gain. Results Compared with children of normal-weight mothers, children of obese mothers had increased risk of asthma (adjusted OR, 1.63; 95% confidence interval [CI], 1.26–2.12) by age 4, and children born to overweight mothers had similar risk (adjusted OR, 1.25; 95% CI, 0.99–1.59). Extreme-low weight gain (<5 kg) and extreme-high weight gain (≥25 kg) were associated with increased risk of asthma; however, the following measures were not significant predictors of asthma: meeting gestational weight gain recommendations of the Institute of Medicine, total gestational weight gain, and weekly rate of weight gain in the second and third trimesters. Conclusion Extreme-low or extreme-high gestational weight gain and maternal obesity are risk factors for early childhood asthma, further evidence of the long-term impact of intrauterine exposure on children and the need to target preconception care to improve child health indicators.