Objective: to characterize lung volumes, airway resistance (AWR), and carbon monoxide diffusion capacity (CMD) in individuals with normal, pre-obese, class I obesity, class II obesity, and class III obesity body mass index (BMI). Methodology: this was a retrospective, quantitative, and cross-sectional study. The sample consisted of 304 individuals of both genders with suspicion or clinical diagnosis of asthma, with BMI ≥ 25 kg/m 2 , and without alterations in respiratory functional tests and 95 healthy and with normal BMI individuals of both genders.