Maternal fish intake during pregnancy may influence the risk of child asthma and allergic rhinitis, yet evidence is conflicting on its association with these outcomes. We examined the associations of maternal fish intake during pregnancy with child asthma and allergic rhinitis. Mothers in the Danish National Birth Cohort (n 28 936) reported their fish intake at 12 and 30 weeks of gestation. Using multivariate logistic regression, we examined the associations of fish intake with child wheeze, asthma and rhinitis assessed at several time points: ever wheeze, recurrent wheeze (>3 episodes), ever asthma and allergic rhinitis, and current asthma, assessed at 18 months (n approximately 22 000) and 7 years (n approximately 17 000) using self-report and registry data on hospitalisations and prescribed medications. Compared with consistently high fish intake during pregnancy (fish as a sandwich or hot meal ≥ 2-3 times/week), never eating fish was associated with a higher risk of child asthma diagnosis at 18 months (OR 1·30, 95 % CI 1·05, 1·63, P= 0·02), and ever asthma by hospitalisation (OR 1·46, 95 % CI 0·99, 2·13, P= 0·05) and medication prescription (OR 1·37, 95 % CI 1·10, 1·71, P= 0·01). A dose-response was present for asthma at 18 months only (P for trend = 0·001). We found no associations with wheeze or recurrent wheeze at 18 months or with allergic rhinitis. The results suggest that high (v. no) maternal fish intake during pregnancy is protective against both early and ever asthma in 7-year-old children.