BACKGROUND Uncontrolled asthma in children is still highly prevalent despite the availability of effective asthma treatment. We investigated 1) the prevalence of uncontrolled asthma among children referred for asthma and referred for atopic diseases other than asthma (ie food allergy, allergic rhinitis or atopic dermatitis) to secondary care; and 2) the predictors associated with uncontrolled asthma. METHODS All children (4 to 18 years) referred for asthma or atopic diseases other than asthma to 8 secondary care centers in The Netherlands were invited to an electronic portal (EP). The EP is a web-based application with several validated questionnaires including the ISAAC questionnaires and the Asthma Control Test (ACT). Children were eligible for inclusion in this study when their parents reported in the EP that their child had asthma diagnosed by a physician. The ACT was used to assess asthma control. Multiple predictors of asthma control (patient, asthma and atopic characteristics) were evaluated by univariable and multivariable logistic regression analyses. RESULTS We included 408 children: 259 children (63%) with asthma referred for asthma and 149 children (37%) with asthma referred for atopic diseases other than asthma. Thirty-nine percent of all children had uncontrolled asthma: 47% of the children referred for asthma and 26% of the children referred for atopic diseases other than asthma. Predictors associated with uncontrolled asthma were a family history of asthma (odds ratio [OR] 2.08; 95% confidence interval [95% CI] 1.34 to 3.24), and recurrent upper and lower respiratory tract infections in the past year (OR 2.40; 95% CI 1.52 to 3.81 and OR 2.00; 95% CI 1.25 to 3.23, respectively). CONCLUSIONS Uncontrolled asthma is highly prevalent in children with asthma referred to secondary care, even if children are primarily referred for atopic diseases other than asthma. Thus, attention should be paid to asthma control in this population.