Objective: To estimate asthma prevalence, severity, and associated factors in adolescents who live in a low relative humidity environment. Methods: In this cross-sectional study, adolescents aged 13-14 years from the city of Petrolina located in the Brazilian semiarid region answered the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. The possible explanatory variables of the study were gender, family income, mother's education, smokers in the household, parental history of asthma, personal history of allergic rhinitis or atopic dermatitis, and physical activity level. Poisson regression analysis was used to assess the association between asthma and the explanatory variables. Results: A total of 1591 adolescents participated in the study, of whom 49.7% were male. The prevalence of active asthma, severe asthma, and physician-diagnosed asthma were 14.0%, 10.4%, and 17.8%, respectively. Adolescents with asthma missed more school days than their peers (33 vs. 22 days/year; p < 0.03). Associated factors that remained significant after adjustment were history of asthma in parents (PR = 2.65, p < 0.001) and personal diagnosis of allergic rhinitis (PR = 1.96, p < 0.001) and/or atopic dermatitis (PR = 2.18, p < 0.001). Conclusion: Asthma prevalence in this low-humidity environment was lower, but more severe than those reported in other Brazilian cities. The dry climate might hamper disease control and this may have contributed to the higher school absenteeism observed. The association of asthma with allergic rhinitis and atopic dermatitis as welt as a history of asthma in parents suggests that atopy is an important risk factor for asthma in this population. (C) 2016 Sociedade Brasileira de Pediatria. Published by Elsevier Editora Ltda. This is an open access article under the CC BY-NC-ND license.