Background: Atopic dermatitis (AD) is a common chronic relapsing skin disease. Genetic variants have been associated with skin barrier function and immune regulation. Thymic stromal lymphopoietin (TSLP), an immune regulator, has been previously associated with AD. Objective: To fine map TSLP and evaluate associations with the onset and persistence of AD. Methods: TSLP variation was determined using targeted massively parallel sequencing in a longitudinal cohort of children with AD. Evaluations included linkage disequilibrium and the persistence of AD for as many as 10 years of follow-up. The association between the presence of AD and rs1898671 variation was evaluated in a second independent cohort. Results: The minor variant frequency for rs1898671 was 23.5% (95% CI, 21.4%-25.8%). This variant was not in linkage disequilibrium with other TSLP variants in the longitudinal cohort (n = 741). White children with AD were less likely to have rs1898671 variant (odds ratio [OR], 1.41; 95% CI, 1.20-1.66) than Genome Aggregation Database controls. Children with AD and the rs1898671 variant during follow-up were more likely to have remission than children who were wild type for rs1898671 (OR, 1.56; 95% CI, 1.26-1.91). In the second cohort (n = 585), the rs1898671 variant was less prevalent in those with AD than those without. The protective effect was greater in rs1898671 heterozygotes (OR, 1.91; 95% CI, 1.34-2.75) than homozygotes (OR, 1.28; 95% CI, 0.61-2.70). Conclusion: TSLP and specifically rs1898671 are important in the pathogenesis of AD and could represent a potential clinical target for the development of therapies to treat individuals with AD.