We examined the association between: 1) cortisol levels and asthma or asthma development; 2) cortisol levels upon stress and asthma. In addition, we performed a post hoc meta-analysis on results from the literature. Cortisol, cortisol upon stress, asthma (doctor diagnosis of asthma and/or symptoms and/or treatment in the past 12 months) and asthma development (asthma at a specific survey while not having asthma at the previous survey(s)) were assessed in the TRAILS study (n=2230, mean age at survey 1 11 years, survey 2 14 years and survey 3 16 years). Logistic regression models were used to study associations between: 1) cortisol (cortisol awakening response, area under the curve (AUC) with respect to the ground (AUCg) or with respect to the increase (AUCi), and evening cortisol) and asthma or asthma development; 2) cortisol upon stress (AUCg or AUCi) and asthma. The meta-analyses included nine case-control articles on basal cortisol in asthma. No significant association was found between: 1) cortisol and asthma (age 11 years) or asthma development (age 14 or 16 years); 2) cortisol upon stress and asthma (age 16 years). The meta-analysis found lower morning and evening cortisol levels in asthmatics compared to non-asthmatics; however, the summary estimates were not significant. We found no evidence supporting a role for cortisol in asthma and asthma development.