Rationale Stress is associated with asthma morbidity in Puerto Ricans (PRs), who have reduced bronchodilator response (BDR). Objectives To examine whether stress and/or a gene regulating anxiety (ADCYAP1R1) is associated with BDR in PR/non-PR children with asthma. Methods Cross-sectional study of stress and BDR (percent change in FEV1 after BD) in 234 PRs ages 9-14 years with asthma. We assessed child stress using the Checklist of Children's Distress Symptoms (CCDS), and maternal stress using the perceived stress scale (PSS). Replication analyses were conducted in two cohorts. Polymorphisms in ADCYAP1R1 were genotyped in our study and six replication studies. Multivariable models of stress and BDR were adjusted for age, sex, income, environmental tobacco smoke and use of inhaled corticosteroids. Measurements and Main Results High child stress was associated with reduced BDR in three cohorts. PR children who were highly stressed (upper quartile, CCDS) and whose mothers had high stress (upper quartile, PSS) had a BDR that was 10.2% (95% CI= 6.1% to 14.2%) lower than children who had neither high stress nor a highly stressed mother. A polymorphism in ADCYAP1R1 (rs34548976) was associated with reduced BDR. This SNP is associated with reduced expression of the gene for the β2-adrenergic receptor (ADRB2) in CD4+ lymphocytes of subjects with asthma, and affects brain connectivity of the amygdala and the insula (a biomarker of anxiety). Conclusions High child stress and an ADCYAP1R1 SNP are associated with reduced BDR in children with asthma. This is likely due to down-regulation of ADRB2 in highly stressed children.