BACKGROUND AND OBJECTIVE: Maternal asthma is a common pregnancy complication, with adverse short-term effects for the offspring. The objective was to determine whether asthma during pregnancy is a risk factor of offspring diseases. METHODS: We studied pregnant women from the Danish National Birth Cohort (births: 1996-2002; prospective data) giving birth to live singletons (n = 66 712 mother-child pairs), with 4145 (6.2%) women suffering from asthma during pregnancy. We estimated the associations between asthma during pregnancy and offspring diseases (International Classification of Diseases, 10th Revision diagnoses from national registries), controlling for potential confounders and validating findings by secondary analyses. RESULTS: Offspring median age at end of follow-up was 6.2 (3.6-8.9) years. Asthma was associated with an increased offspring risk of infectious and parasitic diseases (hazard ratio [HR] 1.34; 95% confidence interval [CI] 1.23-1.46), diseases of the nervous system (HR 1.43; CI 1.18-1.73), ear (HR 1.33; CI 1.19-1.48), respiratory system (HR 1.43; CI 1.34-1.52), and skin (HR 1.39; CI 1.20-1.60), and potentially (not confirmed in secondary analyses) of endocrine and metabolic disorders (HR 1.26; CI 1.02-1.55), diseases of the digestive system (HR 1.17; CI 1.04-1.32), and malformations (odds ratio 1.13; CI 1.01-1.26), but not of neoplasms, mental disorders, or diseases of the blood and immune system, circulatory system, musculoskeletal system, and genitourinary system. CONCLUSIONS: To the best of our knowledge, this is the first comprehensive study of the associations between asthma during pregnancy and a wide spectrum of offspring diseases. In line with previous data on selected outcomes, asthma during pregnancy may be a risk factor for numerous offspring diseases, suggesting that careful monitoring of women with asthma during pregnancy and their offspring is important