||Introduction Preeclampsia reflects an unusual increase in systemic inflammation during pregnancy. We studied associations between preeclampsia and asthma, allergy and eczema in Copenhagen Prospective Studies on Asthma in Childhood2000 (COPSAC2000) and in national registries. Methods COPSAC2000 is a high-risk birth cohort of 411 Danish children. Asthma, allergy and eczema were diagnosed prospectively, and lung function measured at age 1mo and 7yrs. Sensitization was evaluated at age 6mo, 18mo, 4yrs and 6yrs by skin prick tests and IgE measurements. The register-based cohort included 1.7 million children from Danish national registries. Children born to mothers with preeclampsia were analyzed regarding risk of asthma, allergy and eczema in the 35-year-period 1977-2012. Results COPSAC2000: 5.6% (23) was diagnosed with preeclampsia. Preeclampsia was associated with increased risk of treatment with inhaled corticosteroids at age 7yrs; adjusted Odds Ratio (aOR) 4.01 (1.11 to 14.43), p=0.0337, increased bronchial responsiveness to methacholine; adjusted beta-Coefficient log-micromol -0.80 (-1.55 to -0.06), p=0.0348, and allergic rhinitis; aOR 4.83 (1.58 to 14.78), p=0.0057 in the 7-year-old children. Furthermore, the children had an increased risk of sensitization to both aero- and food-allergens, and increased amount of total-IgE during childhood. Registry-based cohort: 3.7% (62,728) were born to mothers with preeclampsia. Preeclampsia was associated with increased risk of asthma, eczema, and aeroallergen and food allergy, especially pronounced after a duration of preeclampsia of >14 days. Maternal asthma increased the risk of preeclampsia. Conclusions Preeclampsia is a shared prenatal risk factor for asthma, eczema and allergy in childhood pointing towards in-utero immune programming of the child.